Stepmania 3.9 by default uses DirectInput, which under Microsoft drivers treats this pad as a standard XBOX 360 game controller, making it suffer from the joystick axes problem. If only one step is down at a time, the controller works normally, but if multiple steps are depressed then the driver reports no steps are depressed. XBCD and XInput have both successfully been used to correct this issue; the former by remapping buttons, the latter by using a software shim between StepMania and the pad.
Follow said steps to correct the issue, or you might just need to go buy a PC pad
XBOX 360 Mat Not working on PC 
