Yes, it's VERY annoying. It happened on our 9200, it happens on our HDR-FOXes, and happens on our Freesat 1010. I don't know if it's Humax specifically or a general dodgyness in the subtitling system. I usually do a back skip (15s) but it sometimes needs a bit of judgement to avoid it doing it again if you go back too far - it seems to happen when there is a long speechless section but the subtitles carry on, so ideally the skip needs to land just before the speech begins.
It does seem less of a problem on HD, but that's not much help really as the places I really need subtitles are on 5USA and the like.