Tvheadend

hello,
I've got a problem with extra time before and after recording ..
Clean install of Xbmcbuntu, tvheadend frontend under xbmc, tvheadend backend maj 3.4.27. Epg with tv_grab_fr_kazer.
what I wanted to do : put extra time before and after eatch records (5 min before, 40 min after)
what I made : put this value on eatch channel first. records start 3 min before, and ends 10 min after.
then, I've removed this values on eatch channel, and put the values on recording/digital video recorder. (set extra time before to 5 and xtra time after to 40.
Same problem, it is ignored, recording starts 3 min before, and stop 10 min after end time.
What can I do to make it work ?
Thanks a lot !
regards, Beber.