You can workaround the issue with the resizing of the page by handling the UserControl.SizeChanged event and closing the ValidationTooltip of the MaskedInput controls. You can use a code similar to this:
sender, SizeChangedEventArgs e)
var validationTooltip = radMaskedNumericInput.FindChildByType<ValidationTooltip>();
However, as the ScrollViewer
doesn't expose any scroll events, I'm not sure which event to suggest you to use to workaround the issue while srolling down/up.
the Telerik team