You already have answer for your problem.
It is a known bug/issue with 6.0 MP1 and 6.0 MP2, so if you want to fix it, upgrade to MP4. I have been using MP4 for around 2 months now and haven't seen any issue. If you do not want o apply MP, you have Workaround too and that is to restart NBU.
Bugs don't follow similar pattern all the time but under some favorable conditions they pop up so very often. May be your catalog size or some new device or other change is providing that favorable condition (If I remember correct you had some disk/filesystem issue).
If I was having this issue, I would patch it to MP4 instead of waiting for 6.5.Message was edited by:
RK