I first noticed this problem with a freeware addon (Flight Design CTSW), but then it happened with the default Goose too.Basically, if I start in the water, one of the wings will dip into the water, sometimes so violently that it catapults the plane into the air.If I land in the water I can control this tendency with the ailerons and violent kicks of the rudder pedals but eventually the plane will be moving too slowly for the control surfaces to have any effect. At which point one of the wings dip into the water, again sometimes with violent effects.However the Beaver doesn't do this, so I'm not entirely sure the sim is at fault...

In the goose - are the wing tip floats down? (3 switches on the overhead panel)