When duplicating PO unable to add POL without closing POL create and clicking Add POL

How to reproduce:
select a PO that has the maximum number of POLs already
Click add POL
When popup appears click "Create new purchase order"
add required details to POL and click "Create PO Line"

Actual: see error toast message that line could not be saved.

Expected: line details are saved and creation screen is dismissed.

Note: if you cancel line creation and start again adding the exact same details to the POL it will save successfully