Here's a 1.20.1 inventory.png over which I have artisanally scribbled:

The output files are pretty much as expected - the normal vanilla files, plus whatever the scribble changed. Notably, nothing outside of the inventory window is carried over into the new copy of inventory.png.

My issue is with the leftovers files, which indicate which parts of a file were split into other files. In the case of inventroy.png and quite a few others, the entire file has a red tint, which is unexpected since, as mentioned previously, all of the empty transparent space in the outer reaches of inventory.png isn't used anywhere in game and isn't carried over into the newly split version of inventory.png.

For comparison, here are copies of icons.png and widgets.png's remainder files, as they appear when you use slicer on default vanilla assets. In this case, none of that unused outer blank area is tinted red, because none of it is actually used. This is what I'd expect for the blank area outside of inventory.png as well, but that isn't the case. Am I misunderstanding what the red shading is supposed to mean, or is this indeed incorrect behaviour?