Sometimes when I heavily hit a pad I get signals on seven other channels and I'm sure there is no mechanical crosstalk between pads. What is going on?
You are using MAX4558 multiplexers without clamping Schottky diodes(bat 85), aren't you? Although MAX4558 has ESD protection,it
doesn't work well when there is overvoltage on inputs and you still
need clamping Schottky diodes. So in reality MAX4558 isn't any better
than a regular 4051 multiplexer.