Finds and Single Table Inheritance

Can someone please help me understand the results that are being
produced when doing queries on a table that is using single
inheritance.

Table1 < ActiveRecord::Base
Role1 < Table1
Role2 < Table1
Role3 < Table1

1. Role1.find(:all) produces:
"SELECT * FROM table1 WHERE type = 'Role1'"

2. any other find on table1 that calls anything but the Role1 Class

EXAMPLES. Table1.find(:all) or Table1.find(:all, :conditions => ['type
= "Role2"]

3. After doing a find like one of the examples from step 2, then do
the original find from step one. (Role1.find(:all))
This now produces the following MySQL:

SELECT * FROM Table1 WHERE type = 'Role1' or type = 'Role2' OR type =
'Role3'

Can someone please help shed some light on what is going on here.
Specifically why is the sql different for the same query??? Thanks