I found the problem. the date range was not exactly overlapping as i had 
thought.  If the range of the 2 time series exactly overlap, then the two 
graphs overlay correctly.  Unless there is another method or package that 
fixes this, it seems that if the 2 time series have non-matching ranges 
(even a small difference will cause a problem), then the 2 graphs do not 
overlay correctly.


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