You can't handle the KeyUp event for RadCheckBox if the key pressed is Enter

When disabled RadRadioButtons should beep their current state.

The following events does not fire:
radMenuComboItem1.DropDownClosing += new RadPopupClosingEventHandler(radMenuComboItem1_DropDownClosing);
radMenuComboItem1.DropDownClosed += new RadPopupClosedEventHandler(radMenuComboItem1_DropDownClosed);
The ComboBoxItem has been replaced with a RadDropDownList. The following events are fired as expected:
this.radSplitButton1.DropDownButtonElement.DropDownClosing += new RadPopupClosingEventHandler(DropDownButtonElement_DropDownClosing);
this.radSplitButton1.DropDownButtonElement.DropDownClosed += new EventHandler(DropDownButtonElement_DropDownClosed);

Coping RadDropDownButton in design time leads to improperly distributed items collection.

Parse event of the property binding is not fired when you change the ToggleState value of RadToggleButton:

Workaround:

private void Form1_Shown(object sender, EventArgs e)
		{
            Binding b = new Binding("ToggleState", vm, "IsToggleSet", true, DataSourceUpdateMode.OnPropertyChanged);
			b.Format += new ConvertEventHandler(b_Format);
			b.Parse += new ConvertEventHandler(b_Parse);
			radToggleButton1.DataBindings.Add(b);
		}

		void b_Parse(object sender, ConvertEventArgs e)
		{
			if (e.DesiredType != typeof(bool) || !(e.Value is ToggleState))
				return;

			ToggleState state = (ToggleState)e.Value;
			e.Value = (state == ToggleState.On) ? true : false;
		}

		void b_Format(object sender, ConvertEventArgs e)
		{
			if (e.DesiredType != typeof(ToggleState) || !(e.Value is bool))
				return;

			bool isToggleOn = (bool)e.Value;
			e.Value = isToggleOn ? ToggleState.On : ToggleState.Off;
		}

RadCheckBox can be checked by the right mouse button

RadSplitButton does not get a focus rectangle when focus by the Tab key. One should first click the action part and then the focus rectangle will appear..

The current workaround is:
public class MyRadSplitButton : RadSplitButton 
{ 
    protected override void OnEnter(EventArgs e) 
    { 
        base.OnEnter(e); 
  
        this.DropDownButtonElement.ActionButton.Focus(); 
    } 
}

Add DefaultItem property in the property grid and allow to set it in design time

Sometimes after rapid clicking on RadSplitButton, its DropDown stops closing when the user clicks outside it.

When a RadCheckBox is in Indeterminate state, the user should be able to see a square instead of checkmark.

Pressing backspace key in ComboBox element added to a RadDropDownButton closes that popup box and doesn't allow you to do any modification

RadRadioButton behaves differently from the Microsoft RadioButton in terms of keyboard navigation.

The mouse right button should not fire the click event of the radbutton. A check should be performed, which only fires the click in case it was clicked by the left button. Possibly, this check should be performed at the TPF level, so it will be available for all controls.

The theme is not applied properly when the button is toggled off.