Well it turned out it's not the hardware with the plugins. I saw the other thread about this and read it was solved with version 1.5.1 but I have the same symptoms at least under Windows 64 bits, X-plane 10.25. I read the workaround about save the flight plan and then load it again. I found another way, using the FMC programmer plugin, if I create a flight with this plugin all is well, the plane stays on course.