Steps to recreate:
open a creative world
obtain a stack of banners
enter survival mode
place a banner
break it
results: the banner does not stack with the other 15 banners
intended results: the banners form one stack of 16
Linked issues
duplicates
Comments

Thank you for your report!
We're tracking this issue in MCPE-43391, so this ticket is being resolved and linked as a duplicate.
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