The last big Tumbleweed update broke opengl on my system. I had to use Xrender to get back my transparency settings.
It turns out that the updated Mesa packages are at fault, reverting back to the pre-update version, solves the problem. There was also an emergency update for Mesa that has already been published to the factory update repos, these packages also work.

Problematic versions are 17.1.6.171.1
Working versions are 17.1.6.170.1 and 17.1.6.173.1

I did not dig deeper which of the Mesa package is at fault.