[not_so_new]

Some of the points above are valid, could be the case.

Let me add to what ebeam said. You can have phase issues with one track micing multiple sources just as you can have phase issues with multiple tracks on a single source. One track can have phase issues if there are issues with the same signal getting to the mic at different times.

For instance (only an example you probably would not do this), lets say you have a singer close to a reflective wall, maybe a glass door or something. The talent has one mic on her so no phase issues right? One track, one mic, one sound source.

Wrong.

Yes one track, one mic but if the reflected signal from the glass door is loud enough you will in effect have two audio sources. Because it is the same "take" you can and probably will have phase issues with the track, the delayed sound will arrive at the mic later then the source sound causing phase cancellations on a single track.

Hope this helps.