+1 on this, I’m UK too I’ve experienced it with both Shield TV and Android mobile for certain HDHomeRun tuner recorded programs. Most things are fine, but the BBCs David Attenboroughs The Perfect Planet is one that exhibits this issue.
I use the same work around as you do.
Edit: at this point I think it might be something to do with 1080 interlaced content (main program) and when the pre-content (adverts/ident) is progressive, or vice-versa, but I haven’t had the time to investigate further.
