The Major Donor constituency is automatically assigned to constituents based on criteria defined in Configuration. Users may choose to count recognitions towards the constituency, and define certain minimum amounts for total giving and single gifts to be assigned this constituency. However, pledges and recognitions don't appear to be counted towards the Major Donor constituency even though they are counted towards the Donor constituency.
Download and install the latest patch, which contains all fixes from previous patches. If you are running an older version, download and install the latest version and then the patch.