What is the significance of a member key unique property for a level ?

If I have a table like this:

col1 int
col2 char(3)
col3 char(3)

with values:
col1 col2 col3
----- ----- ------
1 abc abc
2 abc abc
3 def xyz


I have setup a dimension called def with one level, col3.
The member key is col2 and the member name is col3.

The member keys unique is set to true and the member Names unique is
set to false for this level.

Why doesnt Analysis services complain about the duplicate key values
in col2 column in the database ?

-John.