I think I figured it out!
In an effort to maintain sync, when one EXTRACTS (from V, A or both) PPro will shift the following clips on ALL tracks (not just the selected tracks) earlier in the timeline. However, if there is an overlapping track (a piece of music for instance) where the I/O points are within it but it is not one of the selected tracks, PPro will only shift the tracks so far as to fill a gap further down the timeline and not overwrite that particular clip.
Does that make sense? Probably not. Anyway it makes EXTRACT nearly useless for me.
Thoughts?
Brian