I've marked this against tv_grab_uk_rt but in reality it affects all grabbers using the supplement stuff.
Recently the format of channel_ids files were updated for tv_grab_uk_rt breaking all older grabber versions. These grabbers could have continued to work using a cached version of the channel_ids but the new ids file was forced upon them by the supplement module. (Lost recordings, very unhappy family).
I'm proposing that supplement is changed before the release of the next version of xmltv so that supplement files are versioned. It might mean maintainers have a little extra work (maintaining two or more channel_ids etc) but that the chances of breaking older installs is reduced.