Material ID's in 3ds Max get screwed up?

Hi there,

I’ve been trying to port, rig, and weigh a model, and everything works fine, up until I put in Garry’s Mod and the textures get all messed up.

(Ignore the head, that was fixed and I didn’t take a new picture).

Looking up some fixes, I found that I could force the materials to be set correctly using Material ID’s. The model uses 4 textures: Clothing, attachments, head, and eyes. I set the Material ID’s to go in order from 1 to 4, but the issue comes up when I reach ID’s 3 & 4, the head and eyes. The head ID was set to 3, but when chosen in th Editable Mesh modifier, it only appears in ID #16. Similarly, the Eyes texture was set to ID #4, but only comes up as ID #17.

Any reason as to why this happens?