I checked my 136 ghost times and 134 of them were best times for me. The 2 "slow" ghosts were from the time when HD was originally released. I'm fairly sure of what the reason for this is. I noticed early on when playing the game that if you press the X-button on the result screen before your loyalty points are summed up (which takes about 5 seconds or so) the ghost sometimes get saved even if it is not the best time that you have set on that track. Early on I decided to wait at least 20 seconds before hitting the X-button, I always do that when playing SL or TT. Doing so has resulted in correct ghost saves for over 2 years now. Maybe this is not a solution for everyone out there but it has definitely been a solution for me. The 2 slow ghosts have now been improved to represent best times of course! :)