IF you  canceling the textChanging event of the RadTextBox (e.Cancel = true)  the cursor back at the start of the text.

Work around:

1. Create custom text box element that inherited the RadTextBoxElement. For example:
public class MyTextBoxElement : RadTextBoxElement
{
    private bool isValueChanging = false;
    private int selectionStart = -1;
 
    public MyTextBoxElement()
    {
        this.TextBoxItem.HostedControl.TextChanged += new EventHandler(HostedControl_TextChanged);
    }
 
    protected override void OnTextChanging(Telerik.WinControls.TextChangingEventArgs e)
    {
        base.OnTextChanging(e);
 
        Regex regEx = new Regex(@"[\s]{1,}");
        if (regEx.IsMatch(e.NewValue))
        {
            isValueChanging = true;
            this.selectionStart = base.TextBoxItem.SelectionStart - 1;
        }
         
    }
 
    private void HostedControl_TextChanged(object sender, EventArgs e)
    {
        if (this.isValueChanging && selectionStart >= 0)
        {
            this.isValueChanging = false;
            this.TextBoxItem.SelectionStart = this.selectionStart;
        }
    }
 
    protected override Type ThemeEffectiveType
    {
        get
        {
            return typeof(RadTextBoxElement);
        }
    }
}

2. Create custom Text box that inherited the RadTextBox: For Example:
public class MyTextBox : RadTextBox
{
    private static readonly FieldInfo TextBoxElementFieldInfo = typeof(RadTextBox).GetField("textBoxElement", BindingFlags.NonPublic | BindingFlags.Instance);
 
    public MyTextBox()
    {
        this.ThemeClassName = typeof(RadTextBox).FullName;
    }
 
    protected RadTextBoxElement TextBox
    {
        get { return (RadTextBoxElement)TextBoxElementFieldInfo.GetValue(this); }
        set { TextBoxElementFieldInfo.SetValue(this, value); }
    }
 
    protected override void InitializeTextElement()
    {
        this.TextBox = new MyTextBoxElement();
        this.TextBox.StretchVertically = true;
        this.TextBox.ShowBorder = true;
    }
 
}

3. Use your custom Text box instead the default RadTextBox. 

4. Subscribe to text Changing event of the custom text box and add the following code snippet:

    Regex regEx = new Regex(@"[\s]{1,}");
    if (regEx.IsMatch(e.NewValue))
    {
        e.Cancel = true;
    }

To reproduce:

Add the following line of code: 
[C#]
this.radSpellChecker1.SpellCheckMode = Telerik.WinControls.UI.SpellCheckMode.AllAtOnce;
[VB.NET]
Me.RadSpellChecker1.SpellCheckMode = Telerik.WinControls.UI.SpellCheckMode.AllAtOnce

When you spell check RadRichTextBox and the spell check form is opened click the change button. You will notice that the word will not changed in the original RadRichTextBox.

this.radSpellChecker1.RegisterControlSpellChecker(typeof(RadRichTextBox), new MyRichTextBoxSpellChecker());
this.radSpellChecker1.SpellCheckMode = SpellCheckMode.AllAtOnce;

Workaround:
class MyRichTextBoxSpellChecker : RadRichTextBoxSpellChecker
{
    public override Telerik.WinControls.RichTextBox.Model.RadDocument GetContentAsDocument()
    {
        return (this.CurrentControl as RadRichTextBox).Document;
    }
}

Step to reproduce:
1. Create Windows Forms project  with a form
2. Place RadDateTimePicker control on created form
3. Run application. It will display current date.
4. Click on dropdown arrow to open Calendar
5. Navigate to any month outside of the current date using navigation bar on top of the Calendar, but do NOT select any date
6. Close Calendar without selecting any date
7. Click on dropdown arrow to open Calendar again. Calendar will display current date, which is correct.
8. Now select any date in Calendar
9. Click on dropdown arrow to open Calendar again.
10. Navigate to any month outside of the selected date using navigation bar on top of the Calendar, but do NOT select any date
11. Close and reopen Calendar again. It will display month to which it was navigated in Step 10. Instead it suppose to display selected date

To reproduce:
- set the Mask to P2
- set the MaskType to Numeric
- set the control value to 0.024

The the control displays "2.4" instead of "2.4 %"

WORKAROUND: 
  Private Sub RadMaskedEditBox1_ValueChanged(sender As Object, e As EventArgs)
        Dim control As RadMaskedEditBox = DirectCast(sender, RadMaskedEditBox)
        RemoveHandler control.ValueChanged, AddressOf RadMaskedEditBox1_ValueChanged
        control.MaskedEditBoxElement.TextBoxItem.Text = control.MaskedEditBoxElement.Provider.ToString(False, True)
        AddHandler control.ValueChanged, AddressOf RadMaskedEditBox1_ValueChanged
    End Sub

To reproduce:
- set the Mask to N2
- set the MaskType to Numeric
- set the control value to 4.456789

The the control displays 4.456789 instead of 4.46

WORKAROUND: 
  Private Sub RadMaskedEditBox1_ValueChanged(sender As Object, e As EventArgs)
        Dim control As RadMaskedEditBox = DirectCast(sender, RadMaskedEditBox)
        RemoveHandler control.ValueChanged, AddressOf RadMaskedEditBox1_ValueChanged
        control.MaskedEditBoxElement.TextBoxItem.Text = control.MaskedEditBoxElement.Provider.ToString(False, True)
        AddHandler control.ValueChanged, AddressOf RadMaskedEditBox1_ValueChanged
    End Sub

Symbol characters are process as mnemonics in RadAutoCompleteBox when Italian keyboard is used and non-modifier (Alt or Ctrl) keys are pressed.

1. Create a new project and add RadBrowseEditor.
2. Run the project.
3. Select some folder in the editor.
4. Try to click with the mouse somewhere inside the editor.

Double click on item from auto-complete drop down appends the item twice in RadAutoCompleteBox.

Current behavior:
With decimal places = 2
2.225 is round to 2.22
the proper behavior would be 2.225 to be round to 2.23

Unable to write DateTimePicker/RadMaskedEditBox day part when Culture is set to "tr-TR"

Setting the ActiveMode property does not change the initially selected tab of the RadColorDialog.

RadColorDialog ignores some of the values provided in the overridden GetLocalizedString method. These are for example the tabs of the RadPageView.

NullReferenceException is thrown in RadAutoCompleteBox, when the form is closed and new items are added to its auto complete data source.

When the Office2007Black theme is used, the items in the dialog's page view are not visible. 

Workaround: set the form's BackColor:
((RadColorDialogForm)radColorDialog1.ColorDialogForm).BackColor = Color.FromArgb(103, 103, 103);

RadMaskedEditBox is not able to edit the value when MaskType is set to Numeric, Mask to percentage and CultureInfo NumberFormat CurrencyGroupSeparator is set to "."

Workaround:
CultureInfo ci = new CultureInfo(Thread.CurrentThread.CurrentCulture.LCID, false); //do not use user settings
 
Thread.CurrentThread.CurrentCulture = ci;

Exception is thrown in RadTextBoxControl when the caret blink time is set to none.

RadDateTimePicker/RadDateTimePickerElement should display empty text if the Value property is set to null.

If you put RadTextBox on a form, set its Anchor to Bottom \ Left and you show the form using the following code:
            RadForm1 rf = new RadForm1();
            rf.MdiParent = this;
            rf.WindowState = FormWindowState.Maximized;
            

Themes of RadAutoCompleBoxElement cannot be reused when the element is hosted in RadGridView.

It's not possible to set using code not UI the RadTimePicker.Value when RadTimePicker.ReadOnly = true