This is fixed in Scattered Evil 2.1 and Korax Mod 5.2.

At times, the inventory navigation works as intended, the items in the grid stay in place and you can navigate them in two dimensions. At other times, the items start scrolling to the left and disappear from the grid, similar to how the original Hexen inventory works.

To reproduce the two behaviors, you can either start the game with a “+map map01” argument from ScatteredEvil.bat and it will work the way it is supposed to, or start a new game from the menu. In either case, use the gimme artifacts cheat and you’ll see the difference in scrolling (or not scrolling).