Oh - that would have been nice to know :). I did the test on 4.5 PU2. However I ran the UDF test. Added ""Line No ""(UDF) to PO Detail, PO Work, carried to PO Receipt Detail, PO Receipt/Inv Work and then to AP Invoice Detail and AP Invoice History with bus obj ref on all but the first. Ran a PO Inv receipt and all carried through. It may be that you'll want two UDF, a line no and something else, maybe a date, so that you'll be able to handle users adding/deleting lines. I'm not a BOI expert, not even novice, but would think that with BOI you'd be able to populate the PO detail UDF automagically with the line number.
In version 4.3, if the udf has the same attributes, i.e., name, type it'll carry ti through but PO side and then you can setup the AP side to pull it over.
Make sure if either case the the Line No Udf mask doesn't include a decimal.
Why haven't they upgraded from 4.3?