Problems with accumulated amount due

[Robert G Palmer Jr]

Ok, in playing around (yeah, should have made a copy), I now have one  
customer (me) that, even though, the customer report balance is  
$0.00, the 90+ amount shows up as a positive value.

Here's what I THINK happened, but not sure why I ended up with this  
result.

I UNPOSTED my invoice, and added ONE line item - a $137 credit.  I  
then POSTED the invoice.  That appropriately adjusted the Customer  
Report (CR) balance, but the entry only showed up in the invoice, not  
on the CR itself. So I decided I would undo this.  I UNPOSTED again,  
the same invoice, then deleted this credit, the POSTED again.  I now  
have a balance of $0 in the CR (which is correct), but now the 90+  
amount is showing that I owe $137.

What gives?