Yup. Remember it now. Just north of Crabtree it's way off
the original route.
And now I remember that it was way off south of Pinchot
also. And ... just south of Devils Postpile where the big
burn occurred...
I can post some maps of these areas if you really want...
If you want GPS tracks can do that ...
The 2007 Tom Harrison JMT Map-Pack have all the areas
except Devils routed correctly.

I can't think of any horse/hiker differing sections on
the JMT. In Yose the only horse trails are from
Happy Isles to the JMT connection above the Vernal Falls
Bridge comfort station and a maybe you could call the
connector trail from the stables in TM to Glen Aulin trail.
Seen some horse poo this way/hiker that-a-way in Emigrant.

Have a nice day