Vertex parent disappears when joining meshes? I'm trying to attach a bunch of buttons to a dress. I used vertex parenting for each button and the result looks perfect. However if i join these buttons back to the main mesh (the dress) all the parenting effects vanish.
Is vertex parenting only used for separate objects so that it's useless when they're joined?
And if so, then is there any other good way to rig buttons?
The clothes i'm making are intended to be exported outside of blender, so i can't rely on constraints or modifiers if they won't save on the final result. I'm planning on rigging the dress and the buttons as one mesh in the end, hence the necessity for me to join the two objects.

This is the mesh i'm working on. The buttons are a separate object from the dress.

If i join the buttons with the dress and then use automatics weights on the combined mesh, i get this result. I thought that maybe i can fix it up myself in weight paint mode, but it's really difficult if not impossible to make them align with the dress perfectly.
Ultimately the question is: How do i get the buttons to stick to the clothes for use outside of blender?
If you've the possibility to place the button close to (or just on) a mesh vertex, you can report the bones influences of this vertex to the button.
Here is a magnificent example with a very beautiful dress and no less beautiful buttons:

To do that, once your dress is rigged (and again the button can be placed where a dress vertex is), select the button vertices, and shift select (as active) the dress vertex:

Vertical green stroke indicates the weights of the dress vertex (active).
Use the copy button to report these weights.
The button may deform a bit, but as you want all in one mesh, I think you can't avoid it.
A test case: