Second post just to add...
If I'm JRA and call out ahead to pass, it's because my progress is possibly (or definitely) being impeded. If the rider speeds up, then I no longer have a need to pass as the guy will disappear off into the horizon. If, however, said rider speeds up to prevent my pass only to then slow again (because he can't maintain the pace) and cause me to call out a second time, now I'm a little annoyed. Other than that, it's all good.
-Kedosto