i found a workaround by editing the main class file (the-events-calendar.php in the base plugin directory).
edit the lines as following:
2375: //$this->date = str_replace( substr( $date, 8 ), '01', $date );
2376: $this->date = $date; //<--insert this
it will break in a future update if the devs dont fix the date method, but it works for now :)