We apologize for this inconvenience.
This issue (the problem with IsEnabled="False") is already added in our todo list and we will fix it as soon as possible.
As to the other question connected with the Visibility please verify that you are using the latest released assemblies. I tested this scenario in the following way:
<telerikRibbonBar:RadRibbonTab x:Name="RadRibbonTab1" Header="item1" Visibility="Collapsed">
<telerikRibbonBar:RadRibbonGroup Header="item1" />
Please let us know if you have any other questions or need some more help.
the Telerik team
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