As of this last ladder reset, I noticed something odd about the inv/stash. I will try to explain.

Steps:
1. Open stash
2. Place something in cube
3. Open cube
4. Pick up item from cube
5. Hit escape

Now, here, for over a decade, I remember the entire inventory screen would close, "flash" back to the game, and reopen to be just the stash again. This way you could toggle between cube and stash without dropping the 'picked up' item.
I can still achieve this "flash" by following this sequence:

1. Open stash
2. Open cube
3. Hit escape

The flash occurs and the toggle from stash to inventory is successful. But as of very recently, like no more than 2 months, it no longer allows me to toggle in this way while holding an item.

Has anyone else experienced this?

yep, can be pretty annoying when it doesn't flash back to stash! In my experience, its pretty random whether it goes back to the stash or just to me standing there.

They changed something

Mass tp Books also wont work:(

Yes I have the same problem. Probably some new anti-dupe preventions in place.
Really annoying when your inventory is full and you want to take an item out of your cube and place it directly into the stash.