I'm interested about the recomputation as well.
I
found this KB which seems fairly recent though like almost all Sage KB entries does not specify what version(s) this issue may pertain to:
If you select a master order when creating a purchase Order and hit "Cancel" before/instead of hitting "Accept", that master order will be updated with a zero balance for all remaining lines.
Sage Engineering is currently reviewing
Work Around: Do not "Cancel" PO's with master PO's on them. Instead, hit "accept" on a Purchase order when creating it from a master order and then re-open it and "delete" it.
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Wayne Schulz - Schulz Consulting - 860-516-8990
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