Windows share mounting fails

After upgrading from kernel 2.6.22.9 to 2.6.23.1 without any config changes and CIFS support and all, suddenly when trying to mount the shares fails with (dmesg):

CIFS VFS: cifs_mount failed w/return code = -22

I suspect some kernel changes, probably related to my fstab style, where I had to add password=, though it seemed senseless to make it work in the first place:

//host/share /mnt/mountpoint cifs rw,username=guest,password=,auto,user 0 0

Anyways, aptitude install smbfs solves the problem immediately. Thats weird, as I am sure, that it was previously working without that package..