The Open checkbox on an Other Current Liability register

Hi All

I'm hoping someone can help with a problem related to purchase accruals we're having. When a P/o is received, we have a debit posting to an account "Purchases Received not invoiced" then when the vendor bill (aka supplier invoice) comes in against the receipt, the value is credited back. So far so good. If the bill doesn't come in, no problem , the liability should remain open.

The problem seems to be that the register is showing ALL transactions regardless that the purchase order is effectively balanced (item receipt + billed). What I'm expecting is the "Open" checkbox at the bottom of the register to only show those transactions that are receipts without matching bills. What I've seen is that if the Post Vendor Bill Variances page is used to adjust some for some purchase order that will never be invoiced, then these resulting journals will be hidden/shown based on the "Open" flag.