If I have an entry in my Personal Address book, lets say Smith. John with an email address of jsmith@gmail.com. When I start a new mail message I enter last name of Smith and then use the down arrow to scroll through the entries. I see jsmith@gmail.com but also another entry which shows as Smith, John <j> and the yellow tooltip that pops up shows an email address of just the letter j.

Any ideas? It happens for all the entries in the Personal Address Book but so far I haven't been able to associate any common ground between them.