I am sorry to say but we can not give you a precise answer why this behavior is occurring without successfully replicating it on our side. I have created a sample project in an attempt to reproduce the problem but to no avail. Please review my test project(you can find it in attachments) and tell us what differs in your case. If you could modify it so it reproduces the issue we would be able to determine what is causing it.
All the best,
the Telerik team
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