Comment 2 for bug 596064

Those two lines are about checking if NetBIOS is disabled in smb.conf, and if yes, not start nmbd.
If it works reliably for you once you comment those lines, something must fail on this testparm check.

Could you try running the following (on one of the machines that fail if the check is enabled):
$ testparm -s --parameter-name='disable netbios' 2>/dev/null
$ echo $?

Also, on the machine that fail to start nmbd at boot, does starting up nmbd manually after boot (sudo start nmbd) work with an uncommented prestart script ?