It seems like the first tab of Void Storage is trying to pull items from both itself AND the first bag of your normal inventory (the one that appears to the left of the backpack on the default action bars and to the right of the backpack on the bagnon bag list) at the same time. As an example, the 20th slot in my void storage is empty, but clicking on that empty slot picks up my Rod of Ambershaping (which is in the 20th slot in my first bag)—I get the icon on my cursor, and if I have my actual inventory open, the Rod greys out the same way it would as if I was picking it up to move from that appropriate window. Picking up items in the first 28 slots of my first Void Storage tab and then putting them back down again make the sounds connected to picking up and putting down items in my first bag, though they keep their appropriate icons (picking up items in the 29+ slots don't appear to make the noises of items in my second, third, or fourth bag—all four are Royal Satchels, though I've had this happen on characters with "lesser" bags as well).

This doesn't appear to happen in reverse (clicking on items or empty slots in my inventory doesn't actually pick up items in my void storage, whether I'm at the void storage NPC or not), but does seem to happen whether I have other addons running or not. It continues to occur if I turn the inventory frame off.

I'm running Bagnon 6.0.14.

Fixed!