Steps to reproduce: 
1. Create Telerik WinForms Application and add two RadForm
2. Select one of forms and set the IsMdiContainer property to true 
3. Select the child form. Open the Properties window and set the following properties at design time: 
 - WindowState to Maximized 
 - ThemeName to Windows8 or any other theme 
4. Run the application and show the child form. The child form is cut off instead maximized. 

Workaround: 
1. Reset the WindowState property at design time
2. Subscribe to the Form`s Load event and set the WindowState property 
private void RadForm2_Load(object sender, EventArgs e)
{
    this.WindowState = FormWindowState.Maximized;
}

To reproduce:

private void radButton1_Click(object sender, EventArgs e)
{ 
    StringBuilder detailsText = new StringBuilder();
    for (int i = 0; i < 10; i++)
    {
        detailsText.AppendLine("Line" + i);
    }
    detailsText.AppendLine("END");

   RadMessageBox.Show("Message", "Caption Text", MessageBoxButtons.AbortRetryIgnore, detailsText.ToString());
}

Workaround: enlarge the details section in order to fit the text: 

 FieldInfo fi = typeof(RadMessageBoxForm).GetField("detailsSectionHeight", BindingFlags.NonPublic| BindingFlags.Instance);
fi.SetValue(RadMessageBox.Instance,200); 

To reproduce:

1. Open a RadForm
2. Maximize the form.
3. Restore the form. Then we can see odd line on the bottom of title bar / top of the form.  If you resize the form (make it bigger), new visible areas of form doesn't contain this weird line.

Workaround:
protected override void WndProc(ref Message m)
{
    FormWindowState currentWindowState = this.WindowState;
    base.WndProc(ref m);
    if (currentWindowState == FormWindowState.Maximized && this.WindowState== FormWindowState.Normal)
    {
      
        this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.SizableToolWindow;
        this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.Sizable;
    }
}      

Please refer to the attached project.

Workaround: maximize the form in the Load event.

To reproduce:
- Create new project.
- Make the default  form to inherit RadForm.
- Start the application and maximize the form.
- You will notice that a few pixels are displayed on the right monitor as well.

Workaround:
var screen = System.Windows.Forms.Screen.PrimaryScreen.Bounds;
this.MaximumSize = new Size(screen.Width, screen.Height);

Second Workaround:

public Form1()
{
    InitializeComponent(); 

    this.SizeChanged += Form1_SizeChanged;
}
 
private void Form1_SizeChanged(object sender, EventArgs e)
{
    if (this.WindowState == FormWindowState.Maximized)
    {
        this.Region = null;
    }
}

For the time being to show the grid I would recommend you to use an empty RadStatusStrip.

To reproduce:
Create a RadForm set Maxmize/Minimize box to false. Run it and try to drag the form by clicking on where the buttons used to be.

Workaround:
void MainForm_Load(object sender, EventArgs e)
{
    this.FormElement.TitleBar.MaximizeButton.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
    this.FormElement.TitleBar.MinimizeButton.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
}

Please refer to the attached screenshot.

Workaround: use a RadForm without RadRibbonFormBehavior and hide the FormElement.TitleBar.

To reproduce:

public Form1()
{
    InitializeComponent();

    RadMessageBox.Instance.AutoSize = true;
}

private void radButton1_Click(object sender, EventArgs e)
{
    string msg = string.Format("Test", (sender as RadButton).Name);
    RadMessageBox.Show(msg, "Error");
}

Note that the size of  RadMessageBox is adjusted automatically to display the whole content. Hence, it is not necessary to set the RadMessageBox.Instance.AutoSize property to true.

To reproduce:
-Set RTL via the insane:
RadMessageBox.Instance.RightToLeft = RightToLeft.Yes;

- You will notice that layout is not changed when the messagebox is shown.

Worlaround:
- Use the RadMessageBox show method with the following parameters:

RadMessageBox.Show(this, "test", "caption", MessageBoxButtons.OKCancel, icon, MessageBoxDefaultButton.Button1, RightToLeft.Yes);

RadMessageBox - has incorrect layouts when the message text is formatted with HTML like.

Workaround:

RadMessageBox.Show("Text");
RadMessageBox.Instance.Dispose();

If you are using themes, consider the following approach:
            RadMessageBox.SetThemeName("Windows7");
            RadMessageBox.Show("This is some long text that sometimes does not wrap as it should.");
            var field = typeof(RadMessageBox).GetField("radMessageBoxForm", BindingFlags.NonPublic | BindingFlags.Static);
            field.SetValue(null, null);

To reproduce:

public Form1()
{
    InitializeComponent();
    this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle;
}

Although the user is not allowed to resize the form from the form's borders, it is possible to do it by the context menu.

Workaround:

[DllImport("user32.dll")]
static extern bool EnableMenuItem(IntPtr hMenu, uint uIDEnableItem, uint uEnable);

internal const UInt32 MF_DISABLED = 0x00000002;

internal const UInt32 SC_SIZE = 0xF000;

internal const UInt32 WM_INITMENUPOPUP = 0x0117;

protected override void WndProc(ref Message m)
{
    if (m.Msg == WM_INITMENUPOPUP && (((int)m.LParam & 0x10000) != 0))
    {
        EnableMenuItem(m.WParam, SC_SIZE, MF_DISABLED);
    }

    base.WndProc(ref m);
}

To reproduce:
Use the following method to add a form with a textbox to a panel:
Private Sub AddPage(ByRef f As Form)
    Try
        pnlScreenContainer.SuspendUpdate()
        f.TopLevel = False
        f.Visible = False
        f.Dock = DockStyle.Fill
        pnlScreenContainer.Controls.Add(f)
        f.Visible = True
        f.BringToFront()
        f.FormBorderStyle = Windows.Forms.FormBorderStyle.None
        f.Show()

        f.Activate()
    Catch
    End Try
    pnlScreenContainer.ResumeUpdate()
End Sub

Workaround:
- Use RadTextBoxControl instead.

To reproduce: add a RadForm and start the application.

Workaround:
public partial class Form1 : RadForm
{
    public Form1()
    {
        InitializeComponent();
        
    }

    protected override void OnLoad(Size desiredSize)
    {
        this.ElementTree.InitializeRootElement();
        this.RootElement.ApplyShapeToControl = false;
        base.OnLoad(desiredSize);
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);
        this.RootElement.ApplyShapeToControl = true;
    }
}

To reproduce:
- Add RadMenu to a panel which is docked to the top.
- Add an MDI child and maximize it.
- You will notice that there is one more set of form buttons visible.

Workaround:
- Leave the menu outside of the panel.

To reproduce: 
- Set the MaximizedBounds property so the form takes the entire right part of the screen, the change the windows state at runtime:
private void radButton1_Click(object sender, EventArgs e)
{
    setFormMaximizedBounds(200);
}

private void radButton2_Click(object sender, EventArgs e)
{
    setFormMaximizedBounds(-1);
}
private void setFormMaximizedBounds(int distance)
{
    if (distance >= 0)
    {
        var ownerScreen = Screen.FromControl(this);
        var workingArea = ownerScreen.WorkingArea;
        var x = workingArea.X + distance;
        var y = workingArea.Y;
        var w = workingArea.Width - distance;
        var h = workingArea.Height;
        this.MaximizedBounds = new Rectangle(x, y, w, h);
    }
    else
    {
        this.MaximizedBounds = new Rectangle(0, 0, 0, 0);
    }

    if (this.WindowState == FormWindowState.Maximized)
    {
        this.WindowState = FormWindowState.Normal;
        this.WindowState = FormWindowState.Maximized;
    }
}

To reproduce: use the following code snippet:

public Form1()
{
    InitializeComponent();

    this.radDropDownList1.SelectedIndexChanged+=radDropDownList1_SelectedIndexChanged;
    this.radDropDownList1.Items.Add("TelerikMetro");
    this.radDropDownList1.Items.Add("Windows8");
    this.radDropDownList1.Items.Add("VisualStudio2012Dark");

    this.radDropDownList1.SelectedIndex = 1;

    this.SizeChanged+=Form1_SizeChanged;
}

private void radDropDownList1_SelectedIndexChanged(object sender, Telerik.WinControls.UI.Data.PositionChangedEventArgs e)
{
    ThemeResolutionService.ApplicationThemeName = this.radDropDownList1.Text;
}

1. Use two monitors and decrease the screen resolution to the main monitor.
2. Run the application from the first monitor and move the form to the second monitor.
3. Resize the form on a way to increase the form's height to be greater than the height of the screen resolution of the main monitor.
4. Change the theme. You will notice that that form is resized.

Workaround:

public Form1()
{
    InitializeComponent();

    this.radDropDownList1.SelectedIndexChanged += radDropDownList1_SelectedIndexChanged;
    this.radDropDownList1.Items.Add("TelerikMetro");
    this.radDropDownList1.Items.Add("Windows8");
    this.radDropDownList1.Items.Add("VisualStudio2012Dark");

    this.radDropDownList1.SelectedIndex = 1;

    this.SizeChanged += Form1_SizeChanged;
}

private void Form1_SizeChanged(object sender, EventArgs e)
{
    if (fSize != Size.Empty)
    {
        this.SizeChanged-= Form1_SizeChanged;
        this.Size = fSize;
        
        this.SizeChanged += Form1_SizeChanged;
    }
}

Size fSize = Size.Empty;

private void radDropDownList1_SelectedIndexChanged(object sender, Telerik.WinControls.UI.Data.PositionChangedEventArgs e)
{
    fSize = this.Size;
    ThemeResolutionService.ApplicationThemeName = this.radDropDownList1.Text;
    fSize=Size.Empty;
}

If you have an MDI form with controls anchored to bottom-left, and if the form is shown the following way:

Form form = new ChildForm()
form.MdiParent = this;
form.Show();

private void ChildForm_Load(object sender, EventArgs e)
{
         this.ThemeName = "Office2007Black";
}

the anchored controls will be misplaced.

WORKAROUND:

either set the parent after show:
Form form = new ChildForm()
form.Show();
form.MdiParent = this;

or do not use the Load event to apply theme - use the constructor or the Shown event:

public ChildForm()
{ 
         InitializeComponent();
         this.ThemeName = "Office2007Black";
}

To reproduce:
- Add form and set its AutoScroll property to true. add some controls so the scrollbars appear.
- Dock the form in a smaller window as a MDI child.

Workaround -  Use scrollable panel.

When you have a RadPageViewPage with a TableLayoutPanel inside a RadForm, by changing the theme the TableLayoutPanel is shrinking.

Pleas find attached a sample project.

Workaround: use a ShapedForm instead of RadForm/RadRibbonForm.