1.3 Possible fix for #1139 - Let's discuss it before merging

When I creating a new sales or purchase orders, I always get a specific vendor by default as vendor or customer. It is strange, because that vendor is not a customer.
As I dig deeper, I found the code, where this vendor appears.
I found that, in the Form.pm -> lastname_used() function there was no selector for separating vendor and customers.
Due to that and the content of my oe table (activity) that vendor appeared always, independently of vendor/customer forms.
I fixed it by using a criteria, now I get this default vendor only in purchase order.
Is it a feature or bug to get a default customer/vendor in creating a very new order? Any possible sideffect limiting results?

Anyway, is it a good idea in general to pick up a "random" customer or vendor as default? My opinion it is not.