So a lot of players have recently disabled this because the new default functionality was obnoxious with the way it is flooding the screen with tooltip comparisons at unwanted times (mouseover + SHIFT is still working).
The side effect is as of few days ago it breaks tooltip comparison with storage, such as character bank.
When you first mouseover an item from the bank, there will be no comparison as intended, but even after you press SHIFT, the comparison tooltip does not show up. Instead you need to keep holding SHIFT, mouseover another item and return to the first one to see the tooltip. Pressing SHIFT again does not close the tooltip as intended.
With value of ZERO, the game automatically compares tooltips on vendor gear, but SHIFT is still required to compare from your personal bags and inventory, and that part works just fine.