First I put the items I want to brush into the pouch and keep the bag interface open. Then I throw the bag out with the Q key. I take the items out of the interface. Then I pick up the bag. You will find another item in the bag.

alright sounds reproducible. Can you make sure to add in the version numbers of the mod and minecraft please. Its just good for reference.

My game version is 1.12.2 and my mod version is tinyprogressions-1.12.2-3.3.32-Release.