[OS X TeX] Non superscript comma when using multiple citations with natbib in super mode

[Jeremy]

I am using natbib with the super option and I am having a problem when
using multiple citations with the \citet command.  I have the
following in my file:

\usepackage[super, sort&compress]{natbib}
...
\citet{feynman, einstein}
...

The output gives me "Feynman, et al." and then outputs superscript 6,
non-superscript comma, superscript 7.  For example $^6$,$^7$.  The
trouble is that the comma should also be superscript.

What command should I use to get the comma to also be superscript?  I
am using TeX Live 2009 on my Mac with natbib version 8.31a.

Thanks,
Jeremy Conlin