Starting software - messed up rendering while painting

I bought Armorpaint but can’t use the software: Simply opening the Program and drawing on the default cube results in messed up rendering.
Already opened an issue for this, but no response up to now. Anyone else having these problems? Any ideas?
Here’s the link to my issue on github:

Update: are there any news to this? Anyone else with similar problems?
BTW: Although it works on Linux (not a solution for me), this problem also still persists on both platforms:

So, for me, the software is completely unusable, just a payment of 18$ for nothing.

I am hoping to reproduce the issue, but in the meantime please drop me an email at for a refund.