7k records into Sort node, 4.5m out?

Consider this EXPLAIN ANALYZE output:

    http://explain.depesz.com/s/TCi

Note the Bitmap Heap Scan at the bottom claims to be producing 7094 rows, and the Sort above it expects to be
processing7330 rows (the same number the Bitmap Heap Scan expected to produce)... but the sort is actually producing
4512231rows, which the sort time would indicate is what really happened.  How can this be? 

--
-- Christophe Pettus
   xof@thebuild.com