When clicking on the hourglass button of the customer field, by default accounts are shown. But when you go to the new button a new contact form will open.

As on every other lookup field the new button opens off course the form of the same entitytype.

Although this is a special field, one should think accounts would open up, since this is the default. Now you have to go to the lookup window and click new in there.

This seems like a bug since this was not the case in previous versions.