In javac, the capture of C<? super Object> is C<Object>, not C<CAP>.  More generally, where the declaration-site upper bound is B, C<? super T> maps to C<T> if T = B (we could generalize this to B <: T, since well-formedness already requires that T <: B).

This behavior is unspecified, but could be considered as an enhancement to JLS, since it is longstanding compiler behavior.