It is ridden by a dwarf, yet moves its legs as if a human or elf were on its back. The result is a dwarf jumping up and down on a goat that canters along. OTOH, the sound is exactly that of a mount for the small people.
The Jackpot Goat doesn't have this issue, it runs beneath my dwarf as it should.
this sounds similar to a bug that I've seen before, but not in regards to a specific mount or with dwarves. the only toon I know for sure I've seen it on is my female elf minstrel, and not sure if affected other races/genders. they may have fixed it because I can't recall seeing it recently either. but, in the event that it is the same bug, try toggling your autorun to walk and back (I believe the default key is Insert). that solved the issue in the past (though not permanently, just for a while, perhaps even just for the duration of that ride).