The thinner Klaatu skirts like your one are actually quite delicate and made up of two layers of material bonded together. I suspect this may be the reason why Kenner also made a thicker material version of the skirt; because it was stronger. The thinner skirts on a great many loose Klaatus are simply pulling, if not outright falling apart these days, but I always assumed that was due to play / handling, probably combined with a failure of whatever glue was used to hold the two material layers together. However, I have never heard of or seen this in a carded Klaatu before, where a piece of the top layer of the material has visibly detached itself without the figure being handled! :shock:
Perhaps the skirt glue is also failing on the MOC examples now, but for a piece to apparently fall away like yours has done seems very strange indeed. Maybe you've been really, really unlucky, or maybe this is the fate awaiting all thin skirt Klaatus eventually :-(. I hope not as I have a fair few of them! ;-) (http://starwarsforum.co.uk/viewtopic.php?f=2&t=34008)