Kate Gosselin -- Ducking For Cover -- After Jon's Warning Shot

Jon Gosselin's ex-wife isn't the least bit surprised he fired a warning shot at a photog -- and while she's choosing her words very carefully ... Kate Gosselin seems to be saying she's gotten used to erratic behavior from him.

Kate claims she's not even aware of what happened -- even though it was in the news all weekend -- saying she doesn't pay attention to what her ex does.

But when the camera guy explained what happened she wasn't shocked by Jon's gunslinging, saying ... "Nothing surprises me anymore."

TMZ broke the story ... Jon said he was sending a message when he popped a cap into the air after a paparazzo followed him onto private property.