The diffuse maps works as expected, but the shader just ignores vertexColor (and inverseVertexColor) for the bump maps and they still get applied across the whole model.
For example: in this material, the grass bump appears everywhere so my dirt path has a grass bump pattern visible in it, which does not look good.
textures/darkmod/map_specific/grass4_dirt_01_blend
{
qer_editorimage textures/darkmod/nature/grass/grass4_ed
surftype15
description "grass"
{
blend diffusemap
map tex