Posting Adjustment Vouchers

Can someone help me understand what my expected outcome should be when procecessing an ajustment voucher by pulling in the voucher that has already paid against a PO line.  When I process the credit voucher shouldn't that wash out or open my PO line back up?  Currently What I see happening is we paid a voucher against a PO, we take the credit via adjustment voucher, when we get the rebill invoice and try to post it against the line the new voucher goes into Matched Exceptions.  I am not sure what should be happening when using adjustment vouchers.

I appreciate any guidance that anyone can provide.