Vendor field empty for RE line items in FBL3N

dear all-

I'm experiencing a strange situation. Instead of using the MM-report, I want to do a GRIR analysis in FI. When I run FBL3N for the GRIR account I see that for the goods-receipt related documents (doc type WE) field like puchase order and vendor number are populated (and contain a value). However for the line items that come from the invoice the field purchase order is filled but the field vendor is blank.

I did have a look at the BSEG table for the WE- and RE-related documents: for all line items of the WE document (goods receipt) the fields purchase order and vendor contained a value, for the RE document (invoice receipt) all line items have a value for purchase order but only the first line item (vendor line) has a value for the field vendor. On all the other line items the vendor field is blank.

Looks pretty strange to me, who has a good solution?

thx

Ben