Group in Contextual Tab group - always collapses

I have the following scenario:

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I add a ContextualTabGroup programatically at runtime.

This ContextualTabGroup contains one Tab & one Group.

I add Variants to this Group as follows:

Each button has both a small and large image assigned to their commands.

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As I reduce the width of the window, as soon as the entire group doesn't completely fit, the group drops down to the "Collapsed" variant. It never steps down to Medium or Small. Is there something that I'm missing?

Thanks in advance!