I have a green BTA that has been in my tank about 2 weeks. He moved behind a rock near the back and rarely comes out very much. I have noticed though that his tentacles have shivled up to nearly nothing. When looking at him all you can really see is his base and his shrivled up tentacles. No bubble tips, nothing - it almost looks like he lacks tentacles.
I believe bta's are the natural host to maroon clowns. I could be wrong but I had this problem with an over zealous clown that almost killed a bta by loving it to much. The anemone was to small is mainly the reason but yeah. it's possible for a clownfish to harass a small anemone to the point of not recovering. I'll pm you some pics of mine. I removed it from maroon tank and within two weeks was looking happy and healthy again.