High phosphate and environmental stress are known to cause 'polyp bailout'. Most of the time the coral perishes and does not form a new calcium skeleton. While I've read some claims in books that they can recover in nature I've never seen or heard of it happening in a home aquarium.
Here is what Borneman has to say on the subject:
http://www.reefs.org/library/article/e_borneman3.html