Random Build Buttons Invisible

[NX02]

I've been making my own build buttons for a TMP Federation race, and have just created placeholders until I finish some design elements. The problem is, some of them show up, and some of them don't. The buttons use one 512x512 texture file. I've correctly changed that in gui_global. I've double checked the ship names in the file against the ship file names in the 'Ships' folder. These are the lines that don't show up:

b_sffrig_oberth.......sf_build_buttons.....192 0 64 64
b_sfhd_akula..........sf_build_buttons.....0 64 64 64
b_sflb_miranda.......sf_build_buttons.....128 128 64 64
b_sfhb_excelsior.....sf_build_buttons.....384 128 64 64

All of the buttons are the correct 64 x 64 size, but for an unknown reason these 4 don't show. No white space or anything. Just a blank. Any ideas?