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;