When entering a new Individual into CRM, there are duplicate checks in place. If you add two identical constituents, you are told there is a 100% match, and asked to confirm if there is a duplicate. If you instead add this record as new, all subsequent identical matches will not be pulled in as a duplicate of the first two-- instead, users are asked to choose between any other duplicates within the specified match percentage.
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.