Filter on agenda event are autoselected on "manual event".

htdocs/comm/action/class/cactioncomm.class.php

htdocs/comm/action/index.php

htdocs/core/class/html.formactions.class.php

htdocs/core/lib/agenda.lib.php

htdocs/langs/en_US/agenda.lang

htdocs/langs/fr_FR/agenda.lang