Here is a pretty common scenario - I add someone's address to my favorites using the desktop version of Ovi maps, and then get in my car and drive to that address.
First step. Using the 'find places' option in the desktop version of Ovi Maps I search for my destination address. I then select the correct search result and click the 'add to favorites' option that is presented.
The prompt is now on the favorites label and the street part of the address is selected. The city and postal code are in the (read-only) address part of my favorite. Now I type the name of my destination, e.g. "Bob's place" replacing the street address.
(For commercial destinations this doesn't happen - the street part of the address isn't placed in the label and so easily overwritten.)
When I arrive near Bob's place and look at my phone, I find that the address that I entered is missing and it is giving me the wrong address. This is because my entering "Bob's place" replaced the street address and Ovi maps is now inferring a street address from geo-location (or at least, that's my interpretation of what is wrong).
I would suggest that you need to keep the entire address in the read-only address part of the data consistently - whether it is a known establishment or just my buddy's house.