Why is one requisition for 3 lines, same vendor, get sourced to 3 POs, one line each?

The requisition is fully approved, and ready to source.  The buyer searches for all lines with her id, and selects all of them for sourcing.  Included is one requisition that has 3 lines.  The requisition lines are all for the same vendor.  After the PO create process is done, the buyer goes to add/update POs to see 3 POs created from the one requisition.  Each PO has one line.  All three lines should have been on one PO.

How does this happen?

Thanks,

Shari