TF2 Import Tool won't import DMX flexes

[Pitzik4]

Half a year ago, I made a hat for Team Fortress 2. Since then, I've been intermittently stumbling through errors and bugs in my attempts to get its facial flexes to work, since it has a mustache. I have the shapekeys all set up in Blender. I can export it to DMX and view it in the TF2 Import Tools. The only easy way to test for facial flexes seems to be to watch the character laughing at me, which looked like it was flexing when I screenshotted it. I also tried copying the preview files and then using itemtest. The heavies all ate their mustaches then, so I don't think it worked. I have the latest version of the Blender Source tools (1.10.4), and when I import the DMX back into Blender, the shapekeys come back just fine, looking good as ever. Also, I tried putting the mustache on a Heavy in HLMV, and the flexes work perfectly there, too.

So, to formally state my question, what could be the reason the flexes aren't working in-game? Maybe I'm being too careful, even, and it will be just fine if I upload it now, since they're working everywhere else, but I want to make sure.

Thanks in advance.