Association with a superclass, Link to a subclass

[SKelem]

I'm using Visio 2000 SR1, Enterprise Edition on Win XP sp2.

I have a UML diagram static structure diagram.
In it I have defined:
Class A <- Class B
^
|
<>
Class C
Class A is the superclass of B. (Generalization link/association from A to B).
C is composed of A (Composition link from C to A, navigable from C to A, C may have * A's.)

okay so far.
If I make an object diagram with:
object a: class A
object c: class C
Link from c to a, (double-click on link, set Association to the one between C and A).
okay so far.

But, if I create:
object b: class B
object c: class C
and create the link from c to b (remember b is a subclass of A), the Association box is grayed out, not allowing any association to be chosen for the link!) If c can be contain (have a reference to) an A, then an instance of the derived class B should satisfy that.

Is there a way to fix this in Visio 2000 sr1? A workaround was to change the Static Structure to have C composed of a B, create the link between c and b, set the Association, then move the Composition link from B back to A. But I'd rather have it work properly.