I finally found a way to fix the problem where the images in the inventory are mixed up!! I made it so that minetest doesn't have to generate 3D cube images all the time for stuff in the inventory by setting a 2D inventory image for everything. the images used are all default, so you don't need to do anything except replace the "init.lua" file in \minetest-0.4.6\games\common\mods\default\ and all the images in the inventory should be fixed. It doesn't work for stairs, doors, or any default mods yet, but maybe I will do that soon. Anyway, this is for minetest 0.4.6 only!!!!!!
open the default init.lua file, delete everthing in it, click this link, then copy and paste the code into it: (oh, and don't forget to save it)
http://pastebin.com/drxzBtsT