Thank you for writing.
I have tried a similar scenario to yours and can confirm that buttons added in StartMenuBottomStrip through design-time do not appear at run-time. This is a undesired behavior and we will address it in some of the next releases.
Currently, you could avoid this by adding buttons by code:
|this.radRibbonBar1.StartMenuBottomStrip.Clear(); //use this if you want to remove default buttons
I have updated your Telerik points for bringing our attention on this. If you have other questions, do not hesitate to contact me again.
the Telerik team
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