I made a particle hair system and a vertex group for control its density, but it doesn't seem to have any influence. as you can see in the picture, hairs grow everywhere. I checked if I weight paint the same texture as I use and I don't know, what other reason this could have. I also noticed, that if i add interpolated (doesn't change anything if it is simple children) children, everything works all right, but not in particle edit mode. I tried rendering it and the rendered image doesn't have any hair outside the density group.
One vertex group.
The other vertex group.
If you have multiple vertex group make sure you are viewing and editing the correct one.
Also make sure your blue color is exactly blue. Paint it again to be sure. Zoom in from different rotation angles for nooks and cranies. Rotate the model so you are always facing the mesh face directly while painting. Delete the vertex group, create it again, and use the new name in the Particle System.