This might not have been discovered before, I did a quick online search and didn't see anything. So maybe it's brand new! I discovered it by accident.

What it does: It lets you walk away from the Stash (or Shared Stash) and go to other maps, while keeping the Stash popup window open!

As far as I know, this might not be that useful in a run since I don't think inventory space is ever an issue. But I figured I'd post it here and someone else can figure out if there's anything more to it.

First, open the stash, and go to spells/tomes tab. On your pet spells/tomes, click the X as if you were going to remove one. When it brings up the confirmation window, hit Esc.

It should close the confirmation window and back out and let you move around, but it will keep the stash window open!

The downside is that if you close it, you can't reopen it until you go to the stash again. So you can't, for instance, put Character attributes in after leveling.