Thanks for contacting us and for the reported issue. I have investigated the case and was able to reproduce it on my machine.
It is related to the missing WS_CAPTION style of the form (which actually represents the standard title bar of the form). We removed this style since it causes some visual glitches when doing custom painting in the non-client area of the form.
However, we are going to do some further research on the case and hopefully we will be able to release a fix for it in the next Internal Build that we are going to upload soon.
Please note that the Internal Builds are not entirely tested and we do not provide support for issues introduced in these builds. Their purpose is to simply reflect the current state of our development process.
I hope this is helpful. Do not hesitate to write back if you need further assistance.
All the best,
the Telerik team