MCPE-17178 "Nether Cauldron", which reported the same behavior in Bedrock Edition a couple years ago, was marked Works As Intended.
Nope, you can't shift-click into a full inventory even when something could be stacked with the offhand item.
Even if the inventory isn't full, the game will make a new stack in the hotbar/inventory rather than adding it to the offhand slot.
True, but I still won't be satisfied if the fix for MC-19996 calls them all ink sacs - though "wool dye" would be fine. Bone meal in particular should be listed separately, though, having more uses besides dyeing.
MCPE-17178 "Nether Cauldron", which reported the same behavior in Bedrock Edition a couple years ago, was marked Works As Intended.