Missing track

Odd situation. I'm recording onto a Zoom H4n. Lavalier into left channel, shotgun mic into right channel. Both record fine and i can hear each one distinctly in playback on the Zoom (headphones). I disabled mono mix so they would record separately and I can see that they have different levels as I'm recording. I unplugged each one successively to make sure I was recording them separately.

Imported in FCP X and they come in as mixed audio -- annoying; why not as two separate left and right soundtracks?

Opened in Soundtrack Pro and the different waveforms are clearly there. You can see the gaps when I unplugged each channel. The problem is this: only one track plays back. I can't get the other track to play back on speakers or headphones even though the track is visibly there in the waveforms. Even tried it in Adobe Audition with the same results — one channel is clearly there in the waveforms but does not play back over speakers or headphones. I can play back in other software (such as VLAN) and I can hear that both channels have recorded and play back properly.

Why can't I get both left and right tracks (or 1 and 2 as they are labeled in Soundtrack Pro) to play back? Also, which is which? Is channel 1 left or what?

This test is for some interviews I need to record and I'll be using a wireless Sennheiser and an Audio Technica short shotgun and a wired lavalier which I'll need to mix later on, so it's critical that I figure out why some channels don't play back properly.

I need to get Soundtrack Pro to play back both channels. How can I do that?

Thanks in advance for the advice.

B