Eric,
You are making an assumption that the two issues are the same. This has not yet been demonstrated, although it does seem more likely now. When you use the same material in the same plant, you mostly eliminate calendars, routings, and shipment scheduling, which are common issues in these types of problems.
Anyhow, to summarize:
you did not change any production orders
you did change the MM strategy to 40
the original production order still exists
you did not add any new sales order items,
you did go back into the sales doc in VA02
you did not change any Sales Docs requirement types, or anything else in the sales doc
you did re-run ATP
The sales doc confirmed to a different date.
Please display CO09 under under Strategy 40, then display CO09 under your 'other strategy'.
Best Regards,
DB49