Could you please share how you switch between themes for your RadComboBox?
As a whole, when you wish to switch themes at runtime, you should recreate the UI on the page. This is necessary to force the control to pick up its new theme.
If you changes themes through a DataBinding without reseting your layout, it is likely that your theme will not be applied correctly. This is simply how our theming mechanism works.
I suggest you try recreating your layout after you have changed the theme. Please, let me know if that helps in your case.
All the best,
the Telerik team
Explore the entire Telerik portfolio by downloading the Ultimate Collection trial package. Get it now >>