Sry Guys, I cant really tell where the bug Comes from. I only can tell, that if i set up the OMV everything works (a pure Installation of 1.0.20 omv). In now got aufs work and everything seems to run stable (with NTFS too).
So leads to last possibility, that the Update-Files of OMV are Buggy. Because when I installed the System, I always did those updates - and I had the Problems.
Now I have a clean installed OMV with only aufs, and I didnt used the updates, and everything runs until now.
Seems like those Updates caused the Problems.