ok im back with kernel 2.6.26-2-openvz-amd64
Still the same issue. I could only bring the VE to life by running the script above (in /etc/init.d/vz) manually. 
Its an acceptable workaround, since I dont restart the ve usually.
But there still seems to be a problem tith tty, here the syslog:
Feb 16 13:57:30 mail2 init: tty4 main process (20844) terminated with status 1
Feb 16 13:57:30 mail2 init: tty4 main process ended, respawning
Feb 16 13:57:30 mail2 init: tty2 main process (20843) terminated with status 1
Feb 16 13:57:30 mail2 init: tty2 main process ended, respawning
Feb 16 13:57:30 mail2 init: tty3 main process (20845) terminated with status 1
Feb 16 13:57:30 mail2 init: tty3 main process ended, respawning
is repeated every half a minute!