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Approx. moments by ACI code

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Another engineer in my office has found a discrepancy in the ACI code
for estimating moments in continuous span concrete beams.  Section 8.3.3
allows approximate moments in lieu of a frame analysis for beams and one
way slabs meeting certain conditions.  In particular, the code allows a
value of wl^2/9 for the negative moment at the exterior face of the
first interior support for a two span continuous beam.  After using this
equation and checking using frame analysis, the actual moment appears to
be much closer to wl^2/8.

Has anyone else noticed this?  I would be happy to provide a design
example for anyone who would like to see it.

Dan Vines, EIT
Starzer & Ritchie, Inc.