Which Drupal core function might call SELECT * FROM on custom module table?
If grep/ack-grep can't find a SELECT * (likely) then just add an $debug_query = 'SELECT * FROM {mytable}'; if (substr($query, 0, strlen($debug_query)) == $debug_query) error_log(print_r(debug_backtrace(), TRUE), 4) or match the whole query etc and then look at the Apache error log for the pouring in backtraces. If you dont want to trash the log, log into a file in /tmp.