We have not observed such an issue before. Please, quote the exact version of controls you are using and which of the two controls - RadRibbonBar or RadRibbonView? A list of the dlls you have added and the way you have declared the RibbonUI would also be appreciated.
You can also refer to this article
for a list of the assembly references required for RadRichTextBoxRibbonUI. For example, in the latest version, you should reference:
You should also make sure that the following two assemblies are not
I hope this helps.
the Telerik team
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