Thanks for the detailed reply cny-bikeman. I cannot pinpoint the precise time when the bike started behaving in this manner, but I am fairly certain that it began after I had a crash in a race in October 2011. The problem persisted through the end of the season, and frankly I forgot about it over the winter. I took my bike out for its first hard ride of the season yesterday. I have not changed anything in the way of components or made any adjustments since the end of last season. The reason why this problem has just surfaced now is because this was the first time I took the bike out for a hard ride. I did take the bike out last week for some easy spinning (including hills) and noticed no problems.

Why wouldn't the twisted rear derailleur affetc the shifting when it is on the large front chain ring? It seems that you would have the same degree of twist whether the chain is on the large or small chaniring and so the alignment would be imporper in either case.