By now, you would think they had learned. The Etihad is the stadium which was witness to the most intoxicating last-second drama in Premier League history, the one in which, at the death of the title race last season, a South American's name acquired a least a dozen extra syllables.
So, while the stakes were not as high in this game, you still have to wonder what possessed hundreds of home fans to head for the exits with time still to play and a chance that their team might yet break down Reading's stubborn resistance.
After all, this was the champion team they were abandoning. And to borrow a statement once made about another bunch hereabouts: Manchester City always score.
So it was that yet another lesson was delivered to the early leavers at the Etihad. If not quite an Aguerooooo moment, Gareth Barry's winner in the second minute of added-time might yet have title consequences.
As Roberto Mancini pointed out afterwards, this last-gasp stuff is getting to be a habit. It might not be doing anything for the City manager's blood pressure, but it speaks of an impressive spirit coursing through his dressing-room.
"We won the championship in the last second. Also we have recovered a lot of games in the last three or four minutes. We know we can change every game right at the end. I think that is a very important quality," he said.
His opposite number was less sanguine. Wearing a look which suggested he had just encountered a ghost in the corridors of the Etihad, Brian McDermott was fuming about the goal which had snatched a point from his hands.
As far as he was concerned, Barry had taken an illegal route to power home his header at the far post, using Reading's substitute as if he were a climbing frame.
"I'm just gutted because I don't know how anyone can see that goal differently to how I've seen it – the foul on Nicky Shorey. He was on his back. That's a foul," he fumed.
You could understand the Reading manager's frustration. He was within seconds of avoiding the least coveted managerial role in the game – being in charge of the league's bottom club at Christmas.
Instead, his seasonal fare was yet another low blow to absorb. And this after what was unquestionably the most effective performance since his club were promoted.
Reading defended brilliantly and, although at times it was like the Alamo as City poured men forward, the longer it went on, the longer it seemed the thin yellow line would hold. (© Daily Telegraph, London)