A couple of times, while in "sight range" of a portal, I've had a weird thing happening: tapping on the portal on the map showed it belonging to the opposite faction, but with no resonators attached and no energy remaining. Tapping on its Key instead showed it with the full stack of resonators and at full energy. Is the Intel map dependant on the distance from the portal for the informations? Should I always rely on the keys, when I have them available?
Your client internally calculates the most likely result of your burster firing. Sometimes it is slightly off. It then believes that there are no more resonators, yet it doesn't get a "the portal is now neutral" update from the server. This might be classified as a bug.
The opposite also happens: portals become grey a second before your burster actually fires. This is because the previous burster already killed all resonators, but the update lagged.
NB: yes, distant portals are updated less frequently, but that only applies to those not within burster range (in my experience). That being said, the vagaries of mobile IP often cause strange delays.