[MC-21924] Items do not stack on the correct stack

It seems that items put in a chest by the player with normal item move (left click) are treated different than the ones that are put in by a hopper. Items that are moved into the chest using shift however are treated the same.

So a chest' behavior is as follows:

Items put in using shift-click WILL get topped up by a hopper when it tries to put similar items into the chest.
Items put in using left click WILL NOT get topped up by a hopper when it tries to put similar items into the chest. This is unexpected behavior, the bug.

However if a chest has no more empty slots available then items put in using left click WILL get topped up by a hopper when it tries to put similar items into the chest.

Example

Chest contents:

Coal (40)

A hopper now puts 1 coal in the chest:

Coal (41)

I now move 1 carrot into the chest using left click (placing it in a slot of my choice):

Coal (41)
Empty slot
Carrot (1)

If a hopper now also puts 1 carrot into the chest the contents look like this:

Coal (41)
Carrot (1) <- hopper's carrot
Carrot (1) <- my carrot

The hopper's carrot is placed in the first available empty slot instead of on top of my carrot.