comment spam floating with no associated post

in the past 24 hours I’ve recieved a single comment – from a robot mashup merchant, by the looks. The thing is, I can edit this comment, I can (and have) pull it into moderation, and I expect I can delete it, but I cannot navigate to a post page to which this comment is attached. The edit comments page in my admin area shows no sign of breakage, and is returning null in the place where, in each comment hitherto, the link to the commented post would be. So I’m thinking that something in the comment has deleted, or rendered unreadable, the ID of the post.

My questions are three: anyone seen this before? Anything I can do to protect against it, assuming I’m not going to shut the comments on the blog? And what would be the way to have a look at what’s actually written into my database by this comment?