Unwanted duplication of contacts

[ken]

Another issue we have with outlook is it seems to
duplicate certain contacts when we copy them from
different folders. For instance, I have 50 contacts in
contact folder A and I copy them all into contact folder
B. Without changing any of the contacts in contact folder
B, when I copy them all into contact folder A (and
specify that I want all contacts in contact folder B to
overwrite the contacts in contact folder A), I suddenly
find 65 contacts in contact folder A rather than 50! What
gives?