I have been noticing that on your RadForm there is a problem with how you get your GetDCEx. To keep it short I'll give you a short piece of code that can help you.
(msg.Msg != (int)WindowMessages.WM_NCPAINT)
int flags = (int)(DCX.DCX_CACHE | DCX.DCX_CLIPSIBLINGS
IntPtr zero = IntPtr.Zero;
if (msg.WParam.ToInt32() != 1)
flags |= (
zero = msg.WParam;
return GetDCEx(msg.HWnd, zero, flags);