css files are empty after an update

After an update to the latest typolight version, all old css files are empty when adding new definitions, though the definitions are stored into the database. All old definitions are wiped out, only the header: /* Style sheet xxxx */ remains. New css files remain empty after their creation. I thought it sounds like a permisson problem, but all the css files are writable and the error.log has no entries.

Any ideas?
Thanks Sven

Uhm. What about the execution time? Did you edit any file (including templates) manually? Did you try recreating the templates in the database (deleting everything – don't forget to backup everything!)?