Icing went crinkly on fairy cakes, why?

[SunnyAgain]

I made some fairy cakes, iced and decorated them and they looked lovely. I put them in tupperware-type boxes and the next day the icing had gone crinkly and ridged. It looked as if it had contracted while it was drying. It was glace icing. I've never had this happen before - any ideas?

weird things sometimes happen to icing if it's stil l wet or too watery when you put them in a tin.

was it hard and dry- or not?

I can't remember now! It was at the weekend. I think I would have waited for the icing to dry, but maybe I hadn't left it for long enough. I'm tempted next time I make a batch to put one of the the cakes in a box with the icing still wet and see if it happens again, just so I know if that was the reason!

Did you add a drop of glycerin? It helps keep the icing soft and stops it drying out.