Why did Winterspring turn into a no PvP zone?

Hello!

I noticed today that in Winterspring the opposing faction appears to be "blue", like in shared capital cities such as Dalaran or Shattrath. Nobody can attack anyone. Is this a Christmas Event feature or just a bug? I tried with different characters from both factions, no change. However, in other zones, PvP seems to be undistrubed.

Thanks

I suspect it may be the place where the stairs event is to take place.