I bought 2 pairs of these, (one for myself and the wife) and have tried out both pairs while using my ipod touch at the gym. I haven't noticed any problems as of yet, on the contrary the sound is great and at the price you don't feel bad about beating them up, or sweating into them. Sorry to hear you're having problems I'd return them before your window is up.
Apple started altering the headphone jack length ever so slightly a while back to encourage people to buy apple brand replacements. With some headphones it is more noticable than others. I've had the reverse problem of Apple ear buds not working in headphone jacks of other products as well.
That means you have damaged your headphone jack and slight variances in different headphone's plugs (they are all supposed to be exactly identical but manufacturing tolerances are not great on inexpensive products) is causing poor contact, OR the headphone wire is broken, frayed internally and when it is positioned at a different angle it makes or breaks contact. This is a very common problem that eventually occurs with wear on inexpensive headphones, usually the point where the wire frays is not at the plug end but rather at the earpiece end.