I have exported everything correctly, and set everything right just like in the official tutorials, but when I try to use blend shapes, this bug happens.

Parts of the body/face gets darker when moving the sliders (parts that are not connected to the blend shape)

here is the video showing it:

I'm already using the latest version. I have downloaded it again just to make sure and the error still occurs.

I have purchased the software and a lot of clothing, but it's just not usable with this shape keys bugs/shading bugs.

I'm using the lastest importer version