FYI Igor, we had a lot (90% of our plesk servers) of servers which failed the MU update with the message:
Updating: pp12.0.18-bootstrapper-12.0.18-cos6.build1200150817.13.x86_64 [1/2]
Cleanup: pp12.0.18-bootstrapper [2/2]
Verify: 1/2: pp12.0.18-bootstrapper.x86_64...