Cataclysm Classic. This has been an issue since launch. Factions players are initially neutral with are momentarily hostile when loading. For example, I took the portal from Stormwind to Vash’ir just now and when I loaded into Silver Tide Hollow I was immediately one-shot by a guard. This happens in Moonglade, any Steamwheedle town, Hyjal, Vash’ir etc etc and has been a problem since launch.
Steps to replicate, just port into Moonglade on any character and watch the guards rush you, even if you’re exalted.