Currently I can only make assumptions on what the problem could be. From the provided information I am unable to reproduce the problem on my end and because of that I cannot suggest any possible solution.
It would be helpful if you could prompt the users to share information about:
The exact steps leading to the problem;
What is their operating system?
The used browser and its version;
If IE is used, is it set to quirks, compatibility or standards mode?
Additionally I would also need some details related to the Web Application, like:
The used RadControls version;
The used products on the page and their setup;
Details of implemented Client-side customization, if there are any.
I am looking forward to your reply.
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