Could be a number of things mate. Firstly, check and see the headphones are not physically damaged and even make sure that the microhpones in the in-ear pieces aren't affected by water exposure. Next check the headphones out by moving the wire around while they're plugged in and see how the sound comes out and if the phone reacts to any movements. When I used my phone in water even after hours of drying the headphone jack still wasn't dry so even the slightest movement switched tracks etc. Alternatively, it could be a headphone jack fault in the sense that it may be shorting? Or the 3.5mm 5pin connector on the headphones itself is damaged. It could also simply be a software glitch. Go into "Sounds" in your settings and change what kind of accessory it detects the headphones as. Try "Other", it may solve your problems. Alternatively take it into a Sony store or a phone shop and see if there's anywhere with a similar headset which you could test out.