I have had my Garmin for a long time (2 years) and have never had that problem. Either it is fixed or it is just your unit. Call Garmin. They are very helpful.

As you type in the first few letters of city, it will pull up some defaults to help you from typing the whole thing. Could this be what you mean? If you're having trouble, give Garmin a call, they should be able to tell you if it's a defect.