mmm...i dont know much about this, but perhaps you are using 3D sound for this wavs.
A 3D sound is a mono sound, and is panned according to position of the sound source on the 3D space.
I think there is an option or flag so you can play a wav as a normal Wav, without any 3D transformation, so it should play on stereo, as you saved it.
I hope this can helps you.