So, I checked it and what a trip to the rabbit hole it was.
Rant incomingā¦
There are newer parts of code and older parts of code. In older parts position of an item is transferred as several independent pieces of information - type (character, map, vehicle), position on the map / part of the vehicle, and index. In newer parts of code, position of an item is transferred via item_location, which has all necessary information neatly in one place.
Now, I hijacked the item_location, to additionally carry the information necessary to find correct item regardless of containers it is nested in.
Sadly game code that does dropping from Inventory screen spans throughout several files, many functions, and information about items to drop is conveyed just by index. Which is why the drop function right now drops the bag, as the bag and all items in it share the same index.
It means I would have to alter way too much code to achieve something, that is already possible in Advanced Inventory, which I am not too keen to do.
TL;DR: While it would be nice to have this feature in Inventory screen, complex changes would be necessary, which would make my branch harder to maintain.