I see a similar problem with live TV on LePotato + USB DVB-S tuner (Prof 7500). The recorded DVB stream plays fine but when watching live:
https://www.dropbox.com/s/uyi73jv9mvvlpa6/stutter.mkv?dl=1
I think that Tvheadend server is somehow interfere with video decoding. If Tvheadend server is on another device there is no video stuttering. But when both server and client are on the same device there is massive video stuttering.
With kernel 3.14 there is no such issue.