It seems the contact database is completely independent from the SoldTo ShipTo BillTo fields. The values seems to simply be copied from the Contact Database into the current Document and in no way be linked.
If I make a change in any one of these (SoldTo ShipTo BillTo) fields it should update the contact or at the very least give me the options to copy my changes to the main contact database. This should work both ways.
At the moment once the document has started it seems completely separated from the QW Contact.
Have I missed a trick somewhere?
No, what is designed is intended functionality.
Surely if you want to make changes to the contact/company (to be taken forwards), you would do that in the contact database?
That is not currently possible either.
Adding a maximise button to this screen would be a useful enhancement indeed.