if you put a Store operator inside a parallized Loop, it can happen that directories and entries are duplicated with the same name multiple times. Therefore the Store operator needs to write into a non-existent repository directory. Depending on the timing the directory is created TWICE or even more (depending on number of threads/timing). In this case you have a directory with the same name multiple times. This creates very funny effects when accessing the data...
It seems that the creation of entries is not working synchronized, so that two threads are checking the existence in parallel, both getting a non-existend back and then both create the same entries.
This problem limits the parallizability drastically as we have to switch of parallel execution for all loops writing data!