>>> I think we have been here befor, haven't we Chris?
The words 'Caran' and 'Humax' are inextricably linked in my mind, Caran ;-)
See if the blurb in Section 7.4 of the manual helps:
https://ukfree.tv/documents/retune/Humax_PVR9150T.pdf
If the recording's End Time is set to 'On Time', your box should wait for a signal from the broadcaster until it stops recording, so that's what I'd expect to see there. If it isn't already shown, change the setting to 'On Time'. If 'On Time' is already selected though, try to find an alternative setting which adds a bit of 'padding' to the recording.