I would have to agree with the memory problem. I have been playing with the HK CSL 300 release and the zen theme since saturday (3 days) and just today noticed the side effects of message and call log loss. I went to check my device against a backup and noticed that BB Desktop showed that these databases were completely clear when I went to do an advanced backup/restore. The data is gone forever in my case. I then went to check the memory status of my BB and it said only 1.4 MB free when I usually have about 12 - 16 MB free on my BB :O
Just removed the zen theme but things still don't seem to be back to normal so unless there is some more garbage collection left to free up more memory I may be reloading the FW again.