Vertices not moving in Game

Hi All,
Has anyone come across the following issue.
In 3dsmax there is a pair of vertices under the influence of 2 morphing zones. In 3ds max the zones move these vertices just as I wanted, however in game they refuse to move at all for one of the zones. The rest of the vertices in the same zone move as designed and they also move correctly for the other zone.
I've tried removing both zones and recreating them. The issue always returns on the same two vertices, but necessarily on the same morph zone. If I re-create the zones in the opposite order It seems to be which ever was created last
This is driving me nuts
Have you got any Ideas as to where I can look to solve this?
Has anyone come across the following issue.
In 3dsmax there is a pair of vertices under the influence of 2 morphing zones. In 3ds max the zones move these vertices just as I wanted, however in game they refuse to move at all for one of the zones. The rest of the vertices in the same zone move as designed and they also move correctly for the other zone.
I've tried removing both zones and recreating them. The issue always returns on the same two vertices, but necessarily on the same morph zone. If I re-create the zones in the opposite order It seems to be which ever was created last

This is driving me nuts

Have you got any Ideas as to where I can look to solve this?