[mythtv-users] liveTV ok, recording fails

[Tim Draper]

i've a weird one here guys, not one i've encountered before.

i get tv via a dual DVB-S2 tuner. both tuners use the same scan data. LiveTV works via both tuners, whive i've confirmed by changing source & checking in mythweb > Backend Status to prove that it's obtaining a signal via each tuner.
All channels apart from the UK More4 channel (this is the only channel i've found so far) records fine but this channel always seems to fail recording generating a 0byte file.

according to https://forums.digitalspy.com/discussion/comment/91927478#Comment_91927478, the multiplex shares with channel4 and E4 channels both of which are recording correctly. 

any ideas where the problem might be or where to start checking this type of issue?
iirc i'm running github fixes/29; backend currently reports v29.1-41-gd8a2db7 rather than repo release. I'm possibly due a maintenance upgrade but not sure i want to risk breaking things so soon to xmas - WAF will take an undesirable plunge!