Andrew:
As you suggested, running a Period-End for March 1, 2012 does reset the ATB back to the correct values for a report as at Feb 29 (although I am not sure why).

I was unaware that the data had a Period-End performed on a date later than the Year-End date. (I am going to guess that this was done unintentionally by one of the users.)

I have to recommend you for delving into this matter, and for your detective work on this matter. Thank you for your assistance!