Hello Reinier,
Thank you for writing.
This is a known issue which is already logged in our
Feedback Portal. The issue is resolved and the fix is available in the latest version. Here are this item details:
UI for Winforms Feedback Portal - IMPROVE. RadCheckedDropDownList - unchecking all items is slow.
The issue page contains a workaround for older versions as well.
I hope this helps. Should you have any other questions do not hesitate to ask.
Regards,
Dimitar
Telerik
Check out the Windows Forms project converter, which aids the conversion process from standard Windows Forms applications written in C# or VB to Telerik UI for WinForms.For more information check out this
blog post and share your thoughts.