I sent an answer to the support ticket you sent, but I will post it here as well:
If a Telerik theme is applied to a RadToolBar, then all RadToolBar items (including newly added ones) should inherit this theme. However, if a theme is applied to the RadToolBarTray, it won't be applied to its content.
I prepared a sample project illustrating this behavior. Can you please have a look at it and let me know if it works for you. Also, if I am missing something, please modify the sample to reproduce your issue and I will gladly investigate it further.
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