I was using to bags, on of tier 3 and the other of tier 1. I took my tier 1 bag out of an enderchest and opened. Inside the bag, it was full of items from my other, tier 3, bag, instead of what I had inside it. When I opened the tier 3 bag, it was missing more than half the items, and only had the items that were it the tier 1 bag. I tried putting an item in one bag, and when I opened the other, it had that extra item in it.

I was on minecraft 1.10.2 with forge 12.18.3.2316. I was also in the modpack Age of Engineering on a server