That field is one of the fields on the "Default Values for Purchase Order Entry" dialog in Purchase Order Entry.  A default value should be set there.  The dictionary default value that they have setup in Advanced Field Settings is getting overridden by the value from that dialog which must be blank in their situation.

I can agree with that.  HOWEVER - it's not how it worked in 2016.  I just tested on my own copy, and what you setup in Custom Office came up in PO Entry even if the FOB in the Default was blank.

You are correct, that is how it did work previously.  There was a problem that was fixed where the dictionary defaults were stepping on the values from the "Default Values for Purchase Order Entry" dialog.  

I hate it when a bug works more nicely than a non-bug.  :-(  Alright, I will pass the word along to all of the PO users to setup their Default.