If anyone is interested in this, I found a way to prevent this behaviour.
Find these lines and comment them out as follows:
private function get_terms( $tax ) {
//if ( $this->all_terms )
return get_terms( $tax );
//else
//return QMT_Terms::get( $tax );
}
This of course would be overwritten should a new version of the plugin come out. That is why is never a good idea to change to core files of the plugin. But in case somebody really wants it.