Not All Contacts Come Up Automatically

I've imported my contacts file into Windows Mail but something funny is happening. When I am creating a message and am typing the first few letters of a contact's name, some names come up automatically just as they did in the Outlook but not all of them, although I those names are there on the contacts list. I can't figure out why. In order to add these names I have to go to Tools, Select Recipient and add their names to the TO field. Is there a way I can get Windows Mail to insert all contacts names automatically?