I have tested your scenario and it seems it`s a bug. I have logged it to be fixed by the Developer`s team. I could not give you an exact time for that, but it will be done as soon as possible.
For now, to ensure the usability and accessibility of your application, you could skip the dropdown list decoration using ControlsToSkip property.
Your Telerik points have been updated for the bug report.
the Telerik team
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