Wilburforce - 4:39 pm on Feb 23, 2013 (gmt 0)
seeing these pages (with the wrong comments) appearing in the serps again if I search for them, even though they were all fixed ages ago
I strongly suspect "historic" elements in all this. My own pages have experienced sudden massive drops, then slow recovery, followed by sudden massive drops (...) even though any potential reasons for such a penalty have been long removed, and similar experiences have been reported by several other posters here. It is as if a penalty arising from an earlier state of the page (or of backlinks to it) is being reapplied.
What you report is consistent with my suspicion that historic data are still cached somewhere in Google's massive data-crunching machine, and are periodically reintroduced to current SERPS.