Now if I approach a Stormcloak camp, or come across a Stormcloak patrol in the wild, I get told to back off or else. If I don't, they'll attack. I walked away from one such patrol west of Whiterun, only to have them get into a fight with the Whiterun guards. I don't get this from Imperial camps, and I usually get a warning from a patrol that is escorting a prisoner, but not otherwise. Yesterday I ran into that orc and his two accomplices in Imperial gear (and three naked Imperial soldiers nearby). In the dialog option, the first item was, "I'm in the Imperial Legion and you aren't" or something like that. Weird.
Both miscellaneous quests, "Join the Stormcloak rebellion" and "Join the Imperial Legion" are in my journal. Imperial soldiers advise me to go to Solitude to enlist. I spoke to an Imperial captain and he was more specific: talk to Legate Rikke. I definitely have not spoken to her or Tullius.
The only thing that might have a bearing on this is that I visited Korvanjund that's used in the Jagged Crown quest. I could enter the Temple, but the way inside is blocked by rubble until I get the quest, which I won't have until I talk to Rikke or Galmar Stone-Fist. Even so, I can't see how this would have any connection to the Stormcloaks being hostile.
Unless they are getting impatient for the war to continue, lol.