Lookup field does more than I want

Lookup field does more than I want

I am using the contacts tab and another tab, which I think in the standard CRM is called businesses.  At any rate, when I put someone new into the contacts tab , I use a lookup field for the business in which they work (the business name).  When I find the business name, the mailing address for the business comes through to the person's personal mailing address.  I'm not sure what I did to cause that.  I'm not sure what I can do to fix it, either!  It becomes a problem especially since by the time I'm looking up the business, I've already entered the address information.  

I would thin, there is a problem with 'mapping' the fields, but when I go to look at field mapping in the setup, I don't see that any of the fields are mapped!  Any ideas?