Database is ok, but all data lost...

After editing my feed-sources it's working...

After:

mysql> check table sources;
+-----------------+-------+----------+---------------------------------+
| Table | Op | Msg_type | Msg_text |
+-----------------+-------+----------+---------------------------------+
| selfoss.sources | check | Error | Incorrect file format 'sources' |
| selfoss.sources | check | error | Corrupt |
+-----------------+-------+----------+---------------------------------+
2 rows in set (0.00 sec)

mysql> repair table sources use_frm;
+-----------------+--------+----------+----------+
| Table | Op | Msg_type | Msg_text |
+-----------------+--------+----------+----------+
| selfoss.sources | repair | status | OK |
+-----------------+--------+----------+----------+
1 row in set (0.01 sec)

everything is up and running

From one call to the next I see:
[Fri May 02 16:30:02 2014] [error] [client 127.0.0.1] PDO: Incorrect file format 'sources' in /var/www/apache2/error.log.

Same error after logging in to selfoss.

I changed nothing in my installation, the apache server runs and responds normla to other requests.
I changed the logger level to DEBUG, but nothing appeared in default.log

Anybody an idea ?