Logic Pro (X) continuously sounding notes


I use LX as a virtual synth on a second computer. Protools is running on a first computer and sends midi to the LX computer, output of LX is routed back to protools. Lately I keep getting continuously sounding notes in LX which I each time have to manually kill with an "all midi notes off" command from protools. I do not know if it has anything to do with LX, but I never had this when I was still on L7. Is there some setting in LX which could prevent this from happening?

Thanks, cheers, Bob.