We have tried reproducing this at the PH office but haven't been able to. Please try Rejunky's tip of checking if there are some other processes that interfere with Reason.
The input from the computer keyboard is handled by the same thread (≈process) that handles the GUI, and not by the thread that handles the audio. The GUI-thread always has lower priority than the audio thread, which means that if the computer is working hard, the GUI (and computer keyboard input) might fall behind a bit. This is a design decision, but it might be the cause of the problems that you are experiencing.