Hi Steve,
This situation was never contemplated as a possibility in the origal POA design, so for simplicity and a step beyond DOS - IR you have what you see.

The reason for allowing the said proration of miscellaneous charges was to deal with situations of client's using POA without necessarily having Multi-currency (and using the Misc charge proration as a Multicurrency upcharge or discount), so you can see the assumption that the invoices would be processed at the same time. And some users have taken advantage of the feature for other purposes, such as your situation.

The proration situations described above would not make any difference if the restriction was relaxed, given the proration would go to the Sundry Item GL account, and as long as the PO only included Sundry items or only Regular Items. If it was relaxed I might suggest checking for the line types.

The issue would or could be quite complex for allocations if the PO included both regular items and sundry items, which is why we opted originally to keep it simple.

The designer.
Brian