If you try to split a multi slot when you're over capacity, it won't work.
When you try this near the capacity limit, it won't work either.
- I think it's trying to create a duplicate stack first to split that, which sort off double the volume of that stack (and that makes it seem to go over capacity)
How to reproduce:
# place a multi slot stack in an empty inventory.
# increase the multi slots volume by adding blocks, when it takes in 49.9%, try to split it
# it works
# do the same but try it when you're over 50% capacity used
# it won't work
This makes me conclude that it indeed creates a double multi slot stack somewhere and it uses the volume of both combined to check.
The **exact** same thing happens when you try to move a block into an inventory that has a multi slot where it belongs in.
It will think the multi slot it is going to be merged in counts as double volume which will trigger the "inventory too small" error again. It does compare this to the capacity of the inventory the item is coming from, not where the multi slot is atm.