You could do your stealth action as your standard, but I believe the penalty would reasonably apply until the end of the turn in which you moved more than 2 squares.
That is my interpretation. Currently I can't find RAW on that.
Does teleporting count towards the movement that Warlocks need 3 squares of to get concealment? I mean, I understand they are farther away via the shadow walk, so they have "moved" essentially. But it was instant, and I dunno, doesn't seem like it should count. But that's my gut, my opinion and so I'm asking if I am off via the RAW.