trampenau

I've been using my XH1 for a couple of weeks and have been shooting video. Recently when I shoot in F-Log I cant get the ISO below 800, it will let me choose a higher ISO but when I drop to 800 the ISO turns yellow and wont let me choose a lower setting. Am I being daft or have I clicked an auto setting by mistake I don't know about ? Any help or advise would be great.