The new version 2.10.2 has fixed this bug. Everything imports as it should (with the exception of dmx animations being turned but that's another problem).

Edit Mode -> Mesh -> Faces -> Recalculate Normals did not fix the normals.

Well, until a solution is found and added to the next update, I can only think of 3 workarounds...
Try to force Double-Sided rendering, find all flipped normals and flip them manually, or use an older version of Blender to import the models then work on them in the newer version.

Hello. Been importing models without a hitch for about a year now. However, after upgrading Blender to 2.79 and Source Tools to 2.9.1 I get strange errors.

https://i.imgur.com/5a0MpmO.png

First off, a good deal of the polys seem to be missing. But then I realize that it is just the normals that seem to have been inverted. The problem there is that I have to remember to check the option "Preserve SMD Polygons & Normals" because by default that option is unchecked.

The next problem is that after importing the "reference" model and resize the skeleton (because source models are huge), then import the VTA, appending it to the "reference" (select model not skeleton only and Import), and try something like jaw_open, it seems like only every other vertex responds.

I went back to check other models I've managed to import successfully in the past and the same thing happens to them as well! What has happened?