Curiosity had me. I had to see if I could reproduce it.
I built a sample app just like you mentioned. I ran into a couple of grey areas because you did not describe the mechanics of it fully. So, I made some assumptions.
Here is what it looks like and listed are any (and all - no other actions, or properties were changed) settings for the galleries, form and buttons.
Result - I did NOT see the issue you are having. So, perhaps you have something in an action or other property that is impacting your situation?
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