Tvheadend

I am trying to use this method to get over the situation where there is, for example, a film broadcast in 2 parts with say a 5 min news update program in the middle of it.
Rather than recording 2 parts, I am trying to manually extend the recording to get the film in one "hit" (albeit with the news program in the middle of it)

Scenario

Choose item from EPG and click "record program"
Program ends up in "Current/upcoming recordings" list.
Now, edit the end time of the recording (via "edit" in the the above list). i.e. add 1 hour to the end time
This is fine so far - the recording list shows the amended/extended end time, and the dvr log entry/file for this recording has the correct (amended) stop time within it.

However, reboot tvheadend, and it immediately updates the dvr log file with the original stop time. Hence, my hour recording extension has vanished ...

(This is before any OTA epg updates happen btw)