If you set the OS culture to Dutch (Belgium) and set the Decimal symbol to "." and the Digit grouping symbol to "," you are not allowed to enter 5 digits into the RadMaskedNumericInput control.

MaskedInput focus behaves different when it is set in code behind. When the textbox is on focus and new character is entered the text remains the same and the new character is added at the beginning of the textbox.

Scheduled for:
The fix for this issue will be available with LIB (version 2019.1.128) scheduled for publishing on Monday, 28th January 2019.

Pressing ClearButton of the RadMaskedDateTimeInput will place the caret on the last position.

It must place the caret on the first position. 

When UpdateValueEvent is set on PropertyChanged and the mask uses upper/lower token(s) the letters/characters are updated to uppercase after filling the mask. The control should update its text on every key stroke.

Update:
We are closing this issue because this is expected behavior in MaskedInput.
Value property is updated if all required symbols (required from the Mask) are populated. If you need the Value to be updated on every symbol entered you can set the property AllowInvalidValues = True.

Users sometimes need to invoke Undo / Redo. Public command properties would be a possible way to go.

If Mask = "\A\B\C\D####" (A, B, C, D are escaped) and NumericInput is used. Select All , then typing 1234 produces something like 4312.

Available in LIB version: 2014.3.1222

GridView with GridViewDataColumn.CellEditTemplate.

In it MaskedTextInput is initially Collapsed. Double clicking the Cell will produce a Null refecence exception.

Currently this property works only in MaskedTextInput.

In Q3 2013, Focus() or KeyBoard.Focus() cannot focus the MaskedInputControls so that their Caret is blinking and ready to receive input.
Also, FocusManager.FocusedElement used to do the same  in previous releases but in Q3 it doesn't.

Pasting 5788250000028292 in NumericInput with Mask = # 19 will cut the last digit 2.
Pasting the same number in CurrencyInput will produce an exception.

The MaskedInputExtensions.RestrictInvalidText should allow you to disable entering invalid values. However, if the value is empty and you start typing an invalid character, the text is updated disregarding the RestrictInvalidText setting.

If you try to paste text in the RadMaskedTextInput control using the default ContextMenu, after the Clear button is pressed (or after delete with backspace), the Paste command is not working as expected.

Available in LIB version: 2014.3.1124

Numeric or Currency Input with Value = Null.

Clicking minus key (OemMinus or NumpadSubtract) places minus but Shift + OemPlus (or Numpad Add) does NOT remove the minus sign.

Will be available in Q1 2016 Release.

The 'hh:mm' Mask is not applied correctly in the DateTimeInput when the control is focused.

For example if the date is 2014-05-23, 22:30, and the Mask property of the control is set to 'hh:mm' the displayed text should be 10:30. Currently, this text is displayed only if the input is not focused, otherwise the text changes to 22:30

Currently the MaskedInput controls cannot parse strings containing such full-width symbols.

Actually the .net framework also cannot directly parse such symbols.

Currently users are not allowed to completely remove or customize the Undo/Redo actions in the RadMaskedInput controls. Consider adding extensibility points such as commands or events.

The workaround is to create a custom class which derives from RadMaskedTextInput and override the OnSelectionOnFocus() method.

 protected override int OnSelectionOnFocus(SelectionOnFocus selectionOnFocus)
        {
            if (MaskedInputExtensions.GetCaretToEndOfTextOnFocus(this))
            {
                return this.Text != null ? this.Text.Length : 0;
            }
            if (selectionOnFocus == SelectionOnFocus.Default)
            {
                return 0;
            }
            return base.OnSelectionOnFocus(selectionOnFocus);
        } 
Then you can set the following properties to the mask:
 -  TextMode="PlainText"
 -  Placeholder=" "
 -  maskedInput:MaskedInputExtensions.CaretToEndOfTextOnFocus="True"

The issue is reproducible with NoMask and UpdateValueEvent=LostFocus. The Clear button clears the whole content while deleting with the Backspace and Delete keys leaves the separator symbols. When the focus is moved outside of the masked input, the symbols are removed.

You can subscribe to the PreviewKeyDown event of the control. In the event handler, you can double check if all the text is select and if the delete key is pressed. If yes, you can execute the clear command of the control.

private void TxtPhone_PreviewKeyDown(object sender, KeyEventArgs e)
        {
            var myMask = sender as RadMaskedTextInput;
            if (e.Key == Key.Delete && myMask.Text.Length == myMask.SelectionLength)
            {
                myMask.ClearCommand.Execute(null);
            }
        }

When we use context menu of the control to paste text and the mask is not focused an ArgumentOutOfRangeException is thrown.