[Orgmode] sexp timestamp behavior

[David C. Nelson]

I've been playing around with org mode and I'm confused about the  
behavior of timestamps that are specified using sexps when displayed  
in the agenda. Specifically, if I schedule a TODO and specify a  
timestamp using a sexp, the TODO is not carried forward if it is past  
due.  It does show on the day it was scheduled, but if the TODO is not  
done, the TODO is not carried forward as the manual says it should.
If I don't use a sexp timestamp, the TODO is carried forward if past  
due as expected.
I can't find anything in the manual that suggests sexp timestamps are  
treated differently. Am I misunderstanding something?
Thanks ...