You're listening to just one; Premiere Pro is screwed up in this regard. Monitoring audio in the Source Monitor is limited to one track at a time, be it multi-mono or stereo.
Switch to the Audio Waveform view, and then click the Track selector; it's defaulting to Track 1.
Unfortunately, this only stays active for the current clip. When you're done screaming and swearing, please file a feature request for smarter audio monitoring: Adobe Feature Request/Bug Report Form
Ah, well it's better than not knowing what I was hearing.
I will send in a feature request, Colin. Thanks again.
I have a follow-up question: Let's say I find a section on Track 2 of a four track clip, and I just want to drag Track 2 into my Timeline.
Track Selectors on the left of the Timeline seem to have no effect. If I turn off all but Track 2 Track Selectors on the Timeline, all four channels follow from the source to the timeline, and new tracks are created, which I have to go back and delete afterwards.
How can I just drag one of the four tracks to the Timeline?