Change Tracking Retention Problem

I have change tracking mostly working between two Sql Server Express instances (10.0.1600) .  The remaining problem is how long changes are retained.
The settings on both Express instances are:
retention period = 2,   retention period units = days, auto cleanup = true
Select * from Changetable(Changes ta,0) CT     returns changes all the way back to March 24, 2012. In fact, the last change occurred on March 29, 2012.
I know the above dates by running:
select * from sys.dm_tran_commit_table
Since the current date is 4/7/2012 I expected all changes to have been cleaned up long ago.
Any help/suggestions/comments will be appreciated.
TIA, Joe



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