Just applied the patch and it seems to do the trick. Yipee!
I'm guessing you're just delaying the start of showing subs until some seconds after tuning into the HD channel as I can notice a short delay which isn't the case when tuning into an SD channel.
Subtitles are always sent with a small delay, depends on the broadcaster (between, 0.2 seconds up to 5 seconds). So the first subtitle can appear only after that delay is met (as we don't have a time machine that would fetch us the subtitle bitmaps from the past, before the channel was tuned ).
Quick question: is this is definitive fix and is this only applicable to BBC HD or to all HD channels?
It aplies all the HD channels. There was a time window when no subtitle bitmap had still wrong size info and some optimization code was causing a crash.