I have 4 Flexitots and have been really happy with them for DD3 (4 months). However, the fabric on the inner seems to be 'thinning' and there are bald patches. I bought them in two goes and this is happening to the first lot - the second two have a different colour inner and seem okay - what is going on?? Has this happened to anyone else? Is it because I tumbled them or a manufacturing problem? Any suggestions?