Mesh edges taking on two layer colors at same time

I noticed this first when using a SubD controller mesh, but it also happens with a regular mesh:

  1. Make a mesh (MeshBox in attached) on one layer (color is black)
  2. Change mesh to a different layer (color is magenta)
  3. Use gumball extrude to add sets of mesh faces, new edges are the current magenta layer color, but original mesh box edges are still black. When a regular mesh in shaded mode and not a subD controller, the faces are properly colored, but edges are not.

V5 does not show this behavior.