P43214 Reverse Receipt error: Blanks Invalid

In 9.2, we've seen this a couple times.

Trying to reverse a receipt that was received twice in error. It is not yet vouchered, In F43121, two records with Match Type 1 and only one record with Match Type 2. All same lot number received.

When trying to reverse one of the two receipts, we get a Blanks Invalid error. The cell in the grid for Quantity Not Vouchered is highlighted in red, but I don't know what it is seeing as blank, nor how to fix it.

We also get what seems to be a standard warning for "Reversal for non-vouchered lines only" but it is clearly a warning.