When in a TableView's ViewCell, the user has to use a touch and hold gesture on the control in order for the control to gain focus. Additionally, once the touch is released, the focus is lost.

<TableView>
   <ViewCell>
        <RadMaskedInput>

When the mask is set to be Regex and in code the InputValue of the control is set, the validation is not triggered and the error message is visualized.

On Sony Xperia there is a default Xperia keyboard where the following behavior with MaskedInput is observed:

- while typing into MaskedInput input field, the cursor jumps a few positions; 

For example the control ignores IsTabStop and TabIndex properties for keyboard tab navigation. It behaves differently on Android, iOS and UWP.

MaskedInput ignores VerticalOptions

System.ArgumentOutOfRangeException: Count cannot be less than zero.
Parameter name: count
   at System.String.Remove(Int32 startIndex, Int32 count)
   at Telerik.XamarinForms.Input.MaskedInput.MaskParser.ConstructCandidateTextForMaskTypeRegex(String oldText, Int32 startIndex, Int32 selectionLength, String enteredText, Boolean userDeletes, Int32& insertIndex)
   at Telerik.XamarinForms.InputRenderer.UWP.MaskedInputFormsTextBox.CreateCandidateText(KeyRoutedEventArgs e, Int32& actualInsertIndex)

The issue can be reproduced in SDK Browser application MaskedInput/Features/Regex Mask example IP and email masks when enter symbol like ., @, etc.

The Xamarin.Forms MaskedInput control running on Android with the SwiftKey keyboard app installed does not allow for correct text entry and causes the app to Crash. Using the default keyboard the control works correctly.