Max bones and evelopes driving me mad

[3dway]

I read the help file on skin modifier to see how the envelopes work. It says that a vertex is within the absolute envelope of two bones, they share the weight based on how far into either envelope the vertex is.

I find that I can only have any vertex dedicated to any one bone/envleope.

Say I have one vertex with a bone on either side. I adjust the envelope of bone A until the vertex is 100% controlled by that bone and the mesh shows up the red colouring around it. I now select bone B and try to adjust it's envelope to control the same vertex 100%. I either cannot get bone B to control it, or when bone B has 100% control, bone A loses control.

The help file says that if the vertex is midway between bone A and bone B and absolutely controlled by each, then each bone will share control of the vertex equally. I don't find this to be the case.

I've swithched the control type from absoute to relative and either way I still can't give control to more than one bone.
I've tried painting vertex weights and still if a vertex is controlled by another bone, I can't paint it for the bone I have selected.

What do I have to do to get max to behave like the help file says it should.

What I'm actually doing here is rigging the wing on a dragon model. I have two or three verts between the fingers in the wing. I want to be able to fold up the wings without the vertecies crossing over each other. It seems to me that in order to do this, I have to have them controlled equally by the bones on either side.