I voted "have had problems" but very very little. Kept both together for a very long time and only a few times has the flag tail ever gone down to suck on a Ray. Way I see it is if your Rays are healthy and strong they should be good to retreat if the flag tail becomes bothersome. As well I personally feel that the flagtail is a very busy fish and feels the need to suck almost 100% of the time so if your tank is spotless he might feel the need to pick at fish. My tank is big and has tons of film to suck off so he is busy all day long. Also if a flagtail is gong to go nuts on a Ray and the Ray can't burry its self as protection because you have a bare bottom tank then I can get why the Ray wouldn't be able to retreat. All in all I know I run the risk as many will say. I hope I never find myself in a bad situation.