old age gets to everything......
Some of my old ones have done this too, this is just how it is I reckon! the effects of sunlight/heat/air/cleaners etc over time ,doing what they do with the plastic. My worst affected ones have totally lost their 'cling' now, no amount of soapy water washing etc will get it back. Tack and Peel is now in my polymers drawer permanantly just for this purpose!
I reckon polymers have a shelf life of about 5 years (if you look after them, shorter if you keep them in direct sunlight/on a shelf above a radiator, don't clean them properly etc) Something manufacturors don't exactly shout about!
I have loads of polymers, but if its ever a straight choice between the same image in rubber or polymer, its rubber all the way.May be more expensive, but at least I know I've got it for ever!