@KumasasaI found the problem which coused the black screen for me.In my resourcepack there was the assets/minecraft/shaders folder ( copied from the original 1.8 jar back in 2014).Removing it from the pack solved the problem^^
For me it only happens when a Ressource Pack is loaded by starting the game ( without a pack the worlds are loading fine).
It looks like it has been fixed^^
@Kumasasa
I found the problem which coused the black screen for me.
In my resourcepack there was the assets/minecraft/shaders folder ( copied from the original 1.8 jar back in 2014).
Removing it from the pack solved the problem^^