Under the Hotbar section of Components in the AutoHUD config with the Reveal on active slot content change option set to Yes, dropping an item from the active slot does not reveal the hotbar. This behavior is consistent across dropping a single non-stackable item, one of a stackable item, or a whole stack of items.

Expected behavior: dropping an item would count as changing the active slot and reveal the hotbar.
For AutoHUD 3.2.1

Thanks for the report! Fixed in AutoHUD 4.0.

It turns out that a while ago, that setting stopped having any effect, oops.