I have a duplicate detection rule to check for contacts with the same last name and the same first two letters of the first name, case insensitive. I have checked the box to exclude inactive matching records and I have done no direct database manipulation.
To test the duplicate detection, I created a contact with my name and saved it. I then created a lead with the same last name and Mike instead of Michael for the first name. When I try to qualify that lead and create a contact from it I get a dialog titled Duplicates Detected, but in the bottom where the found duplicates should be it says "Potential duplicate records: None".
This article ( http://support.microsoft.com/kb/2693711 ) is the only thing I've found that seems to address the issue, but it doesn't solve my problem.
Edited to add: I discovered that if I trigger the duplicate detection rule by directly creating a new Contact as opposed to qualifying a Lead, it works correctly and it shows the matched possible duplicates. I'd still like to get it working when qualifying a Lead, however.