2nd lookup on edit always default to null

2nd lookup on edit always default to null

I have two lookup fields that look up to the same form. Basically these two fields allow me to choose users from the same form that contains all my users. Every time I try to edit a record, I find that the 2nd lookup field always default to "-Select-" (it's a picklist lookup). Is this a bug regarding multiple lookup fields looking into the same place?