It's a problem that occurs with acrylic dome ports when sunlight hits the port at a certain angle.
I've seen it when I'm shooting my fisheye zoom and point the camera up towards the surface and sunlight. I don't get it all the time, but sometimes it shows-up. Someone told me glass dome ports don't produce the same issue. The same source suggested the use of black gaffer's tape on the reflected surfaces of the lens eliminate the problem.