transcoding 50Hz 1080i to *50Hz* 1080p

hi all,

i have been testing transcoding in tvheadend.
it works but i cannot get my 1080i@50Hz transcoded to 1080p@50Hz.
it always downconverts the framerate to 25Hz ( by applying yadif deinterlacing with)

does anyone know how to get 50Hz 1080p form 50Hz 1080i ??

thanks,