What are reasons for palys not to have "fringes'?

[Tigé21v]

My green palys all have fringes . Look great. But a frag which I gave to a friend does not fully open anymore (the fringes never extend). He says it never has since he put it into his tank.
Also, I recently got a mixed rock from the LFS, with three paly polyps on it. The palys had no fringes, but it looks like it is starting to get some now (or maybe has always had them, but now slowly starting to extend them?).
What causes this?
BTW, I never target feed them.

 

[Akwarius]

The only time I've seen palys without skirts is when they are retracted or melting. If they are melting some white bleached tissue should be visible. If they are retracted you could try a dip or just wait it out.