Query performance. 7.2.3 Vs. 7.3

While playing with one of my DBs under 7.3 to make use of its better
explain features, I came across a query that runs significantly slower
under 7.3 than
7.2.3. At first, I thought it would be a hardware issue, so i installed both
versions on the same box.
7.2.3 tends to run the query in 80% of the time 7.3 does.
Explain output can be found at http://arch.wavefire.com/72v73a.txt

Please don't hesitate to drop me a line if you require more info.
-Wade Klaver