Have had similar problems with Z1. Something in there just ain't right! My experience is that changing midi-interfaces also changes (and hopefully reduces) the problems. I had notes hanging from the Z1 using an Opcode midi translator pc (2in 2out); this problem was solved when i switched to the Turtle Beach Montego midi-interface, yet another problem occurred (double r?): strange controller data crept in.....weird. Now I use a Midiman Portman 2x4 for my Z1 (and others) and the only problem left now, is that it won't read data, dumped from the machine itself earlier on. I can read other sysex banks etc, bu not the info dumped from my own Z1: "Illegal data received", it says.
Still, I take this bad with the good, I love Z1. Hope things'll work out for you.