Given how much the behaviour varies at different angles and in different positions, we can be fairly sure the algorithm used is incorrect even without these odd cases. You can also see odd orientation-dependent behaviours with non-weird shapes.
To really throw it off and make it stay underwater or hop around, you must be quick to reduce the points and create negative areas via crossover.
But it’s impressive how it lets you draw beyond the boundaries and reacts reasonably.
Best iceberg simulator I’ve ever used. I had fun playing with it for at least ten minutes. I’d go so far as to recommend it for education.