George:
Thanks for you invaluable help on this issue. I am glad that Italy finaly recognized the problem on their keyboards and will be doing something about it soon. Maybe there is an XD9 for me in the future after all, or even perhaps another X1. You are truly a "hands on" person and we are lucky to have you in this forum.
Graham:
I agree, Yamaha does this function the best of all keyboards I know of. As to the problem with the Solton/Ketron boards, the situation presents itself when playing single notes (not multiple as you mention) only they have to be played at a moderate speed and in succession for the condition to manifest itself.
Regards
Mario