Searches resulting in 414 Request URI too long

A few times in the past day I've gotten 414 (Request URI too long)
errors while searching through the mailing list archives. I haven't
figured out a 100% repeatable test case yet, but you can eventually
see what's happening by doing the following:

1. Go to http://archives.postgresql.org/

2. Search for something (e.g., "foo").

3. Move between result pages by clicking Next, Previous, or one of
the page numbers. Do this several times and eventually the URI
gets excessively long. Sometimes it happens right away but
sometimes it requires numerous clicks.

The A tags for the result pages' links go from something like

<a href="?q=foo&cs=utf-8&fm=on&gr=off&st=20&np=1">

to

<a href="?q=foo&ul=http%3A%2F%2Farchives.postgresql.org%2Fpgsql-bugs%2F%25&cs=utf-8&fm=on&gr=off&st=20&np=2">

and then they get longer, with numerous instances of "ul=...".
Eventually they get too long and the web server responds with
414 Request URI too long.

--
Michael Fuhr