Hello Gabor,
We've made some changes to the RadDragAndDropManager recently which may be the reason for the issue.
But I should inform you that RadScheduler is marked obsolete and will be removed from the installation soon. We strongly recommend using our new scheduling control RadScheduleView - it provides more features and better performance, you can check its
demos and
documentation.
Also
this blog post will give you more information about the differences between both controls.
Kind regards,
Yana
the Telerik team
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