thank you, i use exactly the same settings.
The good thing is, i just created a complete new texture from scratch. When i export it as a png an import it into UE4 it will show the alpha as FALSE. I hope this will be the case for all new textures and that the situation will be stable.
I still need to find a solution for my old textures, which i made a longer time ago and where the issue remains. The weird thing is that when i copy the whole texture into a new file created from scratch, the issue will appear again. I thought i can fix it this way and wonder why this is not the case, but for now i will no longer follow this problem.
Thank you again. In the WWW I have not often met a person as helpful as you. I really appreciate this and your very helpful character!