From the Prentice Hall Reference Guide to Grammar and Usage, first ed. (I think there's a new 4th ed. out now), 1991, p. 87:


In the phrase one of those who (orwhich or that) it is necessary to decide whether the who, which or that refers to only one or to the whole group. Only then can you decide whether the verb is singular or plural.

"Rena is one of those shoppers who only buy things on sale."

In this case, Rena is part of a large group, shoppers who only buy things on sale, and acts like them. Therefore, who takes a plural verb because it refers to shoppers.

"The American Dictionary is the only one of the dictionaries on that shelf that includes Latin words."

In this case the American Dictionary is not part of the group. Therefore, that refers back to one and takes a singular verb.

Zat authority enough for y'all, Jackie, CapK and Keiva?