I confirmed this with pgnus 0.97.1
Setting something like (typep "text/plain") to gnus-treat-*
is not working. gnus-treat-predicate does pop for
(typep "text/plain"), and then cadr ("text/plain"). This
always returns nil.

1999-10-07  Yoshiki Hayashi <t90553@mail.ecc.u-tokyo.ac.jp>

	* gnus-art.el (gnus-treat-predicate): Work for (typep "something").