Sigh, comments are currently broken. There is an issue with Serendipity using sequences in PostgreSQL...
I'll hopefully have comments fixed soonish.
Update: Okay, it seems that posting comments from an IPv6 address is beyond the abilities of Serendipity at the moment. I'll look in that sometime soon. It only affects 2 people that I know of, unfortunately one of them is me...
Update 2: Changing the database slightly has resolved this issue.
Bug report on the Serendipity site. It'll be fixed for 1.2 correctly.
