Why is this hair particle system not properly into account the 'density' vertex group? Having trouble with hair particle system on a vertex group on version 2.74.

I have a single head mesh (post mirror-apply, already checked MeshLint and normals) with multires modifier on. I created a beard vertex group to control the area to grow my beard/mustache.



When I specify my beard vertex group under "density", the generated hair only stays in the vertex group area on one half of the mesh, and spreads outside the area and onto parts of the face, neck, and ears in the other half. 



When I specify both "density" and "length" to my beard vertex group, the generated hair does stay in the vertex group area on both halves of the head mesh, but there are glaring bald spots despite having "Even Distribution" toggled on.



I'm hesitant on resorting to replicating and separating parts of my mesh in order to control hair growth, which gives me the expected correct behavior. How do I do this without resorting to this hack?



Not sure if anyone could provide any assistance on my problem.
You should use the Weight Paint mode to create your vertex group.
Make sure you Apply Transforms on your mesh aswell.

Regarding "separating part", creating 'scalps', I think it is a better way to go especially when using animated characters. 



Post a blend file if you still struggle.

EDIT: The Particle tool has a known bug when used with subdivision surfaces, and Multires. So it's "normal" and is being solved.
(SOURCE: https://soundcloud.com/blender-institute/podcast-ep-006-flexirig @ 12:50mn)