Unexpected behavior for inventory GUI

[jasper-bear]

The player/chest/etc. inventory GUI is split up into a grid.
Each slot in this grid has a gray border separating it from the other slots.

When transferring items, clicking on the border between slots unexpectedly results in... no effect.

This is weird and annoying, especially for a new player like me, since this can happen quite easily by accident without realizing that you aren't actually clicking on a slot. There's no indication of an error, and the expected action doesn't occur.

The expected behavior is that it will (like most similar GUIs) simply place the item in one of the slots adjacent to the border the user clicked on. It doesn't really matter which one, just be consistent.