To reproduce: 
- add a RadTextBox with empty Text property but NullText property has some value.
- change the Font style to Microsoft Sans Serif, 8.5pt. As a result the RadTextBox height is decresed a little and the NullText is cut off

Workaround: use Text property instead of NullText and cutomize its ForeColor to gray:
Font newFont = new Font("Microsoft Sans Serif", 8.5f);

public Form1()
{
    InitializeComponent();

    this.radTextBox1.Font = newFont;
    this.radTextBox1.Text = this.radTextBox1.NullText;
    this.radTextBox1.TextBoxElement.ForeColor = Color.Gray;
    this.radTextBox1.GotFocus+=radTextBox1_GotFocus;
    this.radTextBox1.LostFocus+=radTextBox1_LostFocus;

    this.radButton1.Select();
}

private void radTextBox1_LostFocus(object sender, EventArgs e)
{
   if (this.radTextBox1.Text==this.radTextBox1.NullText||this.radTextBox1.Text==string.Empty)
    {
        this.radTextBox1.Text = this.radTextBox1.NullText;
        this.radTextBox1.TextBoxElement.ForeColor = Color.Gray;
    }
    else
    {
         this.radTextBox1.TextBoxElement.ForeColor = Color.Black;
    }
}

private void radTextBox1_GotFocus(object sender, EventArgs e)
{
    if (this.radTextBox1.Text==this.radTextBox1.NullText)
    {
        this.radTextBox1.Text = string.Empty;
        this.radTextBox1.TextBoxElement.ForeColor = Color.Gray;
    }
    else
    {
         this.radTextBox1.TextBoxElement.ForeColor = Color.Black;
    }
}

To reproduce:

this.radSpellChecker1.AutoSpellCheckControl = this.radTextBoxControl1;
this.radTextBoxControl1.Text = "this is a test [doc]";

private void radButton1_Click(object sender, EventArgs e)
{
    radSpellChecker1.Check(radTextBoxControl1);
}

The "[doc]" is underlined as misspelled. However, if you click the button, no mistakes will be found.

Workaround:

char[] punctuation = " .,!?-\\/|~!@#$%^&*()[]_+=;:".ToCharArray();
TextBoxSpellChecker tbSpellChecker = this.radSpellChecker1.GetControlSpellChecker(typeof(RadTextBoxControl)) as TextBoxSpellChecker;

FieldInfo fi = typeof(TextBoxSpellChecker).GetField("punctuation",
    System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
fi.SetValue(tbSpellChecker, punctuation);

When users select the "Ignore All" on the certain word the other ocupation of this word still market as wrong.

example:

Imports Telerik.WinControls.UI
Imports Telerik.WinControls.RichTextBox.Proofing
Imports System.IO
Imports System.Globalization

Public Class Form1

    Dim radTextBox1 As RadTextBox = New RadTextBox
    Dim radSpellChecker1 As RadSpellChecker = New RadSpellChecker

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
        radTextBox1.Parent = Me.Panel1
        radTextBox1.Multiline = True
        radTextBox1.Dock = DockStyle.Fill

        radSpellChecker1.SpellCheckMode = SpellCheckMode.WordByWord



        Dim textBoxControlSpellChecker As IControlSpellChecker = Me.radSpellChecker1.GetControlSpellChecker(GetType(RadTextBox))
        Dim documentSpellChecker As DocumentSpellChecker = TryCast(textBoxControlSpellChecker.SpellChecker, DocumentSpellChecker)
        Dim ms As New MemoryStream(My.Resources.sv_SE
                                   )
        Dim dictionary As New WordDictionary()
        dictionary.Load(ms)

        documentSpellChecker.AddDictionary(dictionary, CultureInfo.CurrentCulture)

        radSpellChecker1.SpellCheckMode = SpellCheckMode.AllAtOnce

    End Sub

    Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click
     
        Me.radSpellChecker1.Check(Me.radTextBox1)
    End Sub
End Class

To reproduce:
- Try to set the  alignment:
radPopupEditor1.PopupEditorElement.PopupContainerForm.HorizontalPopupAlignment = HorizontalPopupAlignment.RightToRight;
radPopupEditor1.Popup.HorizontalPopupAlignment = HorizontalPopupAlignment.RightToRight;

- The property is reset when the popup is opened.

Workaround:
void radPopupEditor1_PopupOpening(object sender, CancelEventArgs e)
{
    RadPopupOpeningEventArgs args = e as RadPopupOpeningEventArgs;
    int width = radPopupContainer1.Width;

    args.CustomLocation = new Point(args.CustomLocation.X - width + radPopupEditor1.Width, args.CustomLocation.Y);
}

To reproduce:
- Set the mask to numeric.
- Change the value and check the Modified property.

- Workaround:
string oldValue = string.Empty;

void radMaskedEditBox1_LostFocus(object sender, EventArgs e)
{
    if (oldValue != radMaskedEditBox1.Text)
    {
        radMaskedEditBox1.Modified = true;
    }
    else
    {
        radMaskedEditBox1.Modified = false;
    }

    oldValue = radMaskedEditBox1.Text;
}

To reproduce:
 radMaskedEditBox1.MaskType = Telerik.WinControls.UI.MaskType.Standard;
 radMaskedEditBox1.Mask = "000-000-0000";

- Paste: 999 999 9999 when there is no selected text.

To reproduce:
- Set the mask like this:
 radMaskedEditBox1.MaskType = Telerik.WinControls.UI.MaskType.Standard;
 radMaskedEditBox1.Mask = "000-000-0000";

- Select the entire content and paste the following: 66677711111

Html formatting does not work as expected in design-time.

To reproduce:
- Drop RadMarkupDialog on the form
- In code set its DefaultFont and show it

WORKAROUND:
Create an instance of RadMarkupDialog prior showing it, not at design time.

To reproduce:
- Change the culture of the RadDateTime picker to Russian.
- Change the month to August and select the month part when the drop down is closed.

Workaround:
radDateTimePicker1.Format = DateTimePickerFormat.Custom;
radDateTimePicker1.CustomFormat = "dd/MMM/yyyy";

To reproduce:
- Set the font for all dates.
- Zoom In and out.

Workaround:
Use the ZoomChanged event and change the font while one zooms as well.

To reproduce:
public Form1()
{
    InitializeComponent();
    AddDateTime();
    radDateTimePicker1.ValueChanged += radDateTimePicker1_ValueChanged;
  
    radDateTimePicker1.Format = DateTimePickerFormat.Custom;
    radDateTimePicker1.CustomFormat = "dd/MM/yyyy HH:mm";

    AddButton();

}

void radDateTimePicker1_ValueChanged(object sender, EventArgs e)
{
    if (radDateTimePicker1.Value.Date.Hour == 0)
    {
        var date = radDateTimePicker1.Value.Date;
        radDateTimePicker1.Value = new DateTime(date.Year, date.Month, date.Day, 23, 59, 0);
    }
   
}

Workaround: 
Refocus the control and the value will be updated.

Workaround: 
((StackLayoutElement)this.radBrowseEditor1.BrowseElement.Children[2]).ShouldHandleMouseInput = false;
this.radBrowseEditor1.BrowseElement.TextBoxItem.RouteMessages = true;

When you focus a RadTextBox you will notice the keyboard button that popups next to the focused control. However, for the RadAutoCompleteBox this keyboard button does not show.

Workaround: show it manually on the GotFocus event and hide it on the LostFocus event 

private void radTextBox1_GotFocus(object sender, EventArgs e)
{
    string progFiles = @"C:\Program Files\Common Files\Microsoft Shared\ink";
    string keyboardPath = Path.Combine(progFiles, "TabTip.exe");
    Process.Start(keyboardPath);
}
 
private void radTextBox1_LostFocus(object sender, EventArgs e)
{
    var procs = Process.GetProcessesByName("TabTip");
    if (procs.Length != 0)
        procs[0].Kill();
}