Well I think it was probably a combination of the cover being bigger so the reader hangs and pulls at the tabs, plus being in my small rucksack and the motion of me walking caused it to "bounce" and flex hence the tabs just collapsed.
But I am going with the silicone cover + a neoprene bag.. this one in fact which may be a bit big but should work well to protect it whilst in my rucksack :
http://www.play.com/PC/PCs/4-/687591...k/Product.html