It doesn't clear the tooltip from *single* stack blocks, including meta items.
If you drag another single stack on a spot that had a single stack on it (same goes if you swap items instead), it's fine and it refreshes.
If you drag a multi slot on that spot, it will keep using the old text.
Sometimes it refreshes correctly though... However if you swap single items with multi slots, then swap them back. Both of them will display the hover text of the single stack.