We have tried to reproduce the issue on our side using the provided by you description and steps, but with no success - it seems everything is working as expected. That is why we would like to ask you for more information about your scenario. Are you using the native WPF TabControl or RadTabControl to place the ComboBoxes inside their tabs? Do you have nested TabControls? Sharing the XAML of your view will also be of great help.
Attached you could find the project we used for our investigation following the provided steps.
Could you please modify the project in order to reproduce the issue - that will help us to better understand your scenario and provide you with the best possible solution?
We are looking forward to hearing from you.
Telerik by Progress
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