Hi, specs are:
Toshiba Portege Z10t running Windows 8.1 (Intel i5), Studio One 4 with latest updates, Yamaha PSR E203 keyboard, generic Midi to USB cable.
Run new external device routine to set up new keyboard with input "USB Midi". Running any virtual instrument (Mai Tai etc) S1 recognises when key is pressed but then maintains that note as a constant drone despite key no longer being pressed.