What I noticed was, the consolidate function starts copying oldest files first.
I had to monitor the new consolidated folder using Win Explorer and display the "Date Created" column.
For me, it stopped after a Carole King album every time.
Then I had to go back and look at the folder itunes was trying to copy files
from, again sorted in Win Explorer by "Date Created" and see what was added to my PC after Carole King. That is how I found the opera album in the compilations folder.
Here is the thread I had started on this problem.
http://discussions.apple.com/thread.jspa?threadID=1481955&tstart=0