I decided to try Nero Linux for burning BD-R discs (Verbatim 25GB, 2x speed) since k3b was failing on some dvd+rw-tools problem. After Nero does a speed test successfully it stops the burning process with the following errors:
Medium format corrupted
HL-DT-ST BD-RE GBW-H20L (H:0 T:0)
Could not perform start of Disc-at-once
This contents were only 21.3 GB so it's definitely not trying to overburn (which is disabled anyway). Does anyone have any ideas what causes these errors? Earlier today I had this same disc in but the error was:
Could not perform end of Disc-at-once
The disc is still considered writeable by both Nero and k3b so there was no data written to the disc.