I made some further testing, by replacing the current glibc and x11vnc packages with the ones from before my dist-upgrade (from snapshots) and found, that the combination new glibc 2.24-8 / old x11vnc 0.9.13-1.2 does not exhibit the problem, while the combination old glibc 2.24-5 / new x11vnc 0.9.13-2 does.
I therefore reassigned this bug report.
