Had one today.  I was maidening a G-44 Widgeon (GP electric twin-engine seaplane) and slowing it down in anticipation of landing or some touch-and-goes.  She has a 28 oz/in sq wing loading and fully tapered wings.  As I lowered throttle at 50 ft to watch the glide characteristics she fooled me and tucked a wing under and went into a beautiful inverted flat spin.  Nothing I tried broke the spin and she landed updide-down with a Splash!  Underpowered for the weight - but scale so I should have known better and kept the speed up. 

Nothing damaged but one nacelle & prop and my pride.  Came down like a maple seed.