Maya doesnt show the "Paint Weights mode", that means if I have the object selected and the tool activated normally the objects shows the black and white areas of the weighting, . But know nothing happens, either blendshape or wire deformer weights are displayed.
But the joints still turn into light blue if I select the influence.
Restart Maya didnt help.
Edit: Another weird thing happens, I testet it on a sphere. If set the value to black and press flood, the sphere disappears, if its grey, the sphere is scaled down 50% and moves (if it has translation values) 50% of the way back to zero. This happens also in other files.