Can't edit last post

It seems post editing is broken, when I edit a post and click submit, I get the following (or simmilar) MySQL error:

SQL ERROR [ mysqli ]

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ': Prosilver style: first impressions WHERE forum_id = 64' at line 1 [1064]

[Edit: see next comment, seems to be limited to last post in thread. Edited subject.]

The weird thing is that I did at one point, between having seen this the first time and now, have been able to successfully edit posts a few times. Not for long, though (long enough to change a post I wanted to change in the first place, not long enough to remove/edit the post I created when first finding I couldn't edit).