That kind of sounds like the voltage to the motor is not being regulated correctly but it may not work the way I think so it may be correct. I am unlikely to have time to check mine out this week but if I get a chance I will.
cheers..I dunno either but I'm thinking that something should regulate the voltage to a constant then it goes to the pot to set the speed, just now it seems like it's just passing straight through (maybe not STRAIGHT through) , found it strange that there was no change in anything with all 3 wires disconnected from the pot
the plug on the control board that the pot wires go to have the earth too so motor stops if disconnected...should be no difference disconnecting the pot tho?