>* This does not work, no error gets shown, but the replace command
>* does not put anything in the field
>REPLACE prceng.prcpqtyby2t WITH THIS.LIST(THIS.LISTINDEX,1)
>
>* This works
>SELECT prceng
>REPLACE prcpqtyby2t WITH THIS.LIST(THIS.LISTINDEX,1)
>
>Is this a bug, feature, or my misusing a replace on a table that is not selected?

There's been an ongoing problem with REPLACE when you're in a work area with no table/cursor/view open in it, or where the record pointer is positioned past EOF(); could that be the probelm here?