Selecting cover on manage images doesn't work

Hi,
found an unecspected behaivior when i have multiple gallery relations and try to select a cover image. that won't be saved. Only error message
Strict warning: Only variables should be passed by reference in theme_node_gallery_api_manage_items_form() (line 59 of ...\sites\all\modules\node_gallery\theme\theme.inc).

Thanks for that module!