Yeah ... I can kind of see why they do it. With Ultra, you are sometimes "off" the top of the waves (flying) even though you are stationary. You can see this happen sometimes in slew. Suddenly the plane takes off when you go to slew while sitting stationary in high waves. So it is "seeing" you flying and with the gear down, it looks like they've built in an "error" that crashes you landing with the gear down on water. So when you "peak" ... at that instant you are "flying" and if the gear is down, the plane sinks.
I'm using Ultra all the time with the boats, it is fascinating. But when flying the floats, I keep it one notch down from ultra and there are no problems. We shouldn't be taking off in seas with 6 foot waves anyway! :-)
So you are right about the liferaft! I had the problem while slewing around trying to fix a location scenery. Suddenly there seemed to be a hole in the water and down I went. When I got off ultra ... it didn't happen. So I think the above may be what is happening. Again no big deal, but interesting.
Doug