I just misspelled one of the options in one of my plugins:
qa_opt('cached_qcount');
instead of correct version:
qa_opt('cache_qcount');
The result: In the database in table qa_opt I found a newly created entry:
"cached_qcount" with value "1048576"
Can this be considered a bug?
PS: function qa_db_set_option($name, $value) can be found in qa-db-options.php