They are umbrella-ing i think he means. They do that and almost flip inside out and then they cant close up anymore either.
Not sure why they do it. I have had them do it before also and attributed it to low trace elements and high n03 po4 levels. I noticed that after a period of extream growth in my tank and no water changes. I was just dosing mag/ca/alk. I started vinegar/vodka dosing and dosing trace elements too and they came around. But again, this is all anecdotal.