I had a stack of 100 invisibility pots in my shared bank. I put them into a player's backpack, split the stack into fifties, and then put one stack of fifty back in the shared bank. Then I ran several more quests and then logged off for the day.
Today, when I logged in, at the top of my shared bank (most recent deposits) is a stack of 50 invisibility pots and a stack of 100 invisibility pots.
I'm 99.9% certain there was only one stack of 100 in my shared bank when I took it out yesterday.
Very strange.