Strange shape key behavior

I have 2 identical meshes one with shapekeys the other not.
If i xfer a shape key it works fine but if i select a single face on the mesh been exferred to and seperate it from the main mesh i can then rejoin it using alt m to reattach the vertices without having changed its position at all so mesh should be exactly as it was but when i try xfer the shape key again its now all messed up

I tried the same thing on the body as the shapekey is only for the face and it still messed up.
Just tried doing a remove doubles and the shapekeys work when done that way so thats dumb i joined the verts the exact same way that remove doubles did
I deselected a larger area and rejoined with the doubles command and this time the shapekeys failed in the sme manner as when i joined by hand

So why is this happening?Seems illogical

Shape keys depend on the internal order of vertices. Think of it as a stack. If you remove something from the middle of the stack, then add it back, it gets added back at the bottom(top?) of the stack, which completely fouls the order. If you remove a single face, but it doesn’t remove any vertices, the vertex count and order doesn’t change. If you add that face back and remove doubles, you might get lucky and have it work, but don’t count on it.

EDIT: I don’t know if I was clear… Shapekeys only affect vertices! Vertex order is how the vertex data is ordered in the internal database, and has NO connection with how the shape appears on screen. If the vertex count and order are the same, shapekeys should transfer properly. Any edit which deletes or adds vertices will almost always change the vetrex order

Thx fo r the reply Skpfx guess that makes sense.
is there anyway to restack it in the correct order?

I remember seeing an add-on somewhere that did that, but if I remember right it didn’t work in current blender versions. Can you post a link to your file? I might be able to help you get it sorted out.

Thx for the offer but its already deleted:( I will in future apply shapekeys first and ask questions after:) I notice i can make changes without messing the already applied shapekeys