I think we are in an area where you have to say that "it depends".

I know that flaps on sailplanes will lift the nose unless some down trim is mixed in or inputed. Other modelers have reported neutral pitching. And now you are saying that it wants to tuck.

I think it's a case of how wide the wing chord is relative to the tail length and area. Any airfoil with positive flap in going to show some negative pitching moment at the same time it wants to lift. If the chord is narrow the tail has the leverage to resist the nose down pitch and the extra lift lifts the nose. If the chord is wide the extra lift is overpowered by the pitching moment of the airfoil if the tail and tail length are not sufficient to counter the pitching action.

At least that's my story and I'm sticking to it...