VF with minimal STAT table produces weird behavior on Windows

I'm attempting to export a variable font from a designspace file using the following command
`fontmake -m MyDesignSpace.designspace -o variable`
The output works well on almost every place (Mac, adobe, html) but in windows something weird happens, every style name is Regular, I couldn't find an arg or command to fix this problem, so I want to know if it is a bug or is just my script.
Thanks