Depending on the amount of time he/she had them they should have browned a little before receeding being light deprived. Bleaching should have been from too much light and little nutrients. If it receeded overnight after getting it that day then no way it was light. I may have missed...
I always look at it like this. If you have them on your front glass so prominant than I'm sure you have them on the bottom, side glass, back glass, rock etc. That shouldn't hurt too much. I have them breeding also, and I usually scrape them off...
I would probably be looking into lowering your nitrates that could be the culprate of the rtn. Also you may want to test for phosphates. This could also be a problem.
Don't worry about it, caps seem to slime alot, and the A. Youngei is named "Slimer" becuase it is a slime producing machine.
It may take a couple of days to get good polyp extension too, so be patient, lol.
Got any pics?
I am in the same boat as curtis. Except I had a hippo tang for about 6 months + and added a large yellow tank and a large swallowtail angel. No problems even from the beginning. I personally think it's not a bad thing unless they aren't getting fed well, but if you feed them and keep the tank...
They are called Asternia stars. Melev talks about them on his website. If they have a blue hugh they could be coral eaters, but if they are just brown they are grazers etc. I have them and they seem to be beneficial to the tank. HTH's a little.
If your wanting nice color patterns etc. With a fowlr:
I like the idea of maybe 3 medium yellow tangs, blue cheak trigger, halequin tusk, emperor angel, then adding last a clown trigger. I would exclude one of those, but I was just giving some ideas and some of my faves...
You may like a candycane coral, frogspawn, hammer, brain, pretty much any lps. You may be ok with a bta or rbta. In softies I like rics, and zoos about it.