Rails - Jul 2005 - activerecord single table inheritance: find(:all)

Hi folks-
I''ve got a problem with ActiveRecord and STI. I have several classes
("Sample", "LaserCapture") which are descended from a common
ancestor
"Datum" using STI on a table named "Data". Standard CRUD
operations
work fine here with one exception: doing Sample.find(:all) returns all
objects descended from "Datum", not just Samples. Why does this happen
and how can I deal with it?