but what is the poi

In T80090#1004164, @Bastien Montagne (mont29) wrote:

There is no bug here, vertex parenting works by index, so if you change topology or number of vertices with your modifiers, you should expect such parenting to be broken.

but what is the point of breaking vertex parenting? in one version it worked with mask modifier then you removed the support so it is not some technical limitation it is your preference. i was using it to parent a custom eyeball to geometry of eyeball from an alembic file, but because i need to make original/parent eyebal invisible and geometry is in parallel and close proximity cycles transparency was not handling it well so mask modifier did the trick.

i dont get it, it would not made anything worse if you left the feature in. it is useful in some cases