another 8.1->8.4 regression

I'm having problems with another one of my queries after moving from 8.1.19 to 8.4.2. On 8.1.19, the plan looked like this:

http://wood.silentmedia.com/bench/8119

That runs pretty well. On 8.4.2, the same query looks like this:

http://wood.silentmedia.com/bench/842_bad

If I turn off mergejoin and hashjoin, I can get 8.4.2 to spit out this:

http://wood.silentmedia.com/bench/842_better

...which it thinks is going to suck but which does not.

The query and relevant table definitions are here:

http://wood.silentmedia.com/bench/query_and_definitions

Any suggestions? I'm guessing the problem is with the absurd over-estimation on the nested loop under the sort node, but I'm not sure why it's so bad.