Here is the pic I refered to earlier.
And it states:
Mounting a (22"/24") tire on a (22.5"/24.5") rim can cause severe injury or death. While it is possible to pass a (22"/24") diameter tire over the lip or flange of a (22.5"/24.5") size diameter rim, it cannot position itselp properly against the rim flange. If an attempt is made to seat the bead by inflating the tire, the tire bead will break with explosive force.
I think that that is pretty damn clear to what they are trying to say.