Thanks for contacting us and for the provided screenshot.
Unfortunately, without a sample Windows Forms application that reproduces the issue we will not be able to provide you with decent support.
Therefore, I would like to ask you to send us a small project that we can use to directly investigate the case and find the reason for the undesired behavior.
Please note that you will have to open a new support ticket in order to be able to upload files.
Thanks for your time.
I look forward to receiving the details requested.
the Telerik team