Initially I had 2 shape keys for my eyebrows which I used as a driver using a bone z location (-3*var and 3*var). This worked fine. But now I wanted to create a third shape key. So after that I added this key to the same driver bone using expression 6* var. But this does not work. Seems like only 2 shape keys work at a time using this setup. Can anyone explain it to me why so?