I'm trying to install new icons for potions, but for some reason they're not showing up in-game. The default unmodded icons are showing up, instead.

I have the following files:
Tx_potion_bargain_01.tga
Tx_potion_cheap_01.tga
Tx_potion_exclusive_01.tga
Tx_potion_fresh_01.tga
Tx_potion_quality_01.tga
Tx_potion_standard_01.tga

and I put them in:
*/Morrowind/Data Files/Icons/m/

But, instead of overwriting the default potion icons, I get the originals instead. What's going on here? I made sure that "TryArchiveFirst=0" is in Morrowind.ini.