The tank shouldn't be sprinting if the healer is lagging behind. It used to be fine to do this since the healer could Sprint to catch-up, but now if the tank sprints the gap between the tank and the healer isn't going to shrink.

And before anyone mentions that the healer should just keep up, remember that healers often have relevant things to cast between pulls like a shield on the tank, or the healer might be pre-casting a DPS spell on the target the tank is going to pull. All of these things require standing still so healers will generally lag slightly behind the tank so before a tank hits sprint it's generally a good idea to at least check if the healer is close by first.