They are known jumpers. I bought a flasher from Big Al's yesterday and while the girl was trying to catch one for me two tried to jump out (unsuccessfully). I've had a blue sided wrasse for a while and he managed to get into my overflow. He lived there for a day while I tried to figure out how to retrieve him but then went down the standpipe and into the sump on his own. I have since put some of the reflective silver eggcrate on my tank as a cover and haven't had any problems. This eggcrate doesn't block any light as far as I can tell.
HTH
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