Thank you for providing us with detailed information about your scenario. Now I can see where your issue origins from. I will try to clarify how you can achieve your requirement.
I can see that the default Style of the RadButton control is extracted and you have customized it. Your custom style works correctly when it is applied to the RadButton control because most likely you have used the default template of the same control as base extend it and to create your custom Style.
However, when customizing Styles you need to have in mind that every control providing users with different functionality has different style. This means that you need to extract the default style of the RadDropDownButton and apply your customizations to it as well. By following this approach you will be able to achieve your requirements. Basically, changing only the TargetType property of your custom Style is not enough to apply it to a completely different control. It is highly possible that the other control has different visual states that visualize/hide different parts of the visual representation of the control.
Please try to apply your customizations to the default style of the RadDropDownButton and let us know if you need any further assistance.
Pavel R. Pavlov
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