(IDS 9.3, Unix)

I need help. I've configured ISM so, that it makes backups to file system. It's no problem, but now I have mounted Network File System. I this case, backup behave very strangely.
When I write:

onmode -cl it backups the first logical log, but second times device loses his label .... and backup can't finish. I must unmount, relabel and again mount the device. But it also backups only first log (or first db_space .. when I use onbar -b -w -L 0)

I dont know what to do ...