Just to echo what Pau said: it's totally normal to claim something if you think it looks interesting and then decide later on that it's not for you! (I do it all the time.) A lot of time something that looks easy turns out to be a nightmare...

Just comment on the bug and let us know if it looks like you aren't going to be able to get to it and we can unassign it. (The bot doesn't handle unclaiming, alas.)