This is an oldie but a goodie.
I get this about once per year, when I have to do some survey drafting. The last time it occurred on 2007 and I had some seriously wigged out geometry. No one could say why (not the big dogs either).
It happened again, and with brutally simple geometry; no overlapping segments.
The Arc length is good, but notice the Chord length in the label.
In the Parcel Geometry Vista the chord information is correct, but using a report, the Chord is erroneous, like the label.
The solution is to kill the bloody curve and recreate it. This is rarely a solution when you have complex parceling.
I am hoping someone will have a better answer or solution that we have already heard. If you come up with something, please post it.