Came back and checked to see if I could saddle it up and ride it, and it appears to be the case. Doesn't have a slot for armor though.
I made a new bug report because this is still happening and it was marked as resolved...I can no longer vote for this because of the "resolution" though
Shown in the screenshots, you can see that the skeleton trap horses spawn in the mushroom biome and are also rideable mobs.
I'm the one that reported this and now I can't update it because it's saying I wasn't the reporter. The issue seems to be gone in 16w44a, however.