If you place a fence (any type) on the side of a block and then attach a fence to the top of that fence (Object A in image). When you walk up to that fence, you pop up a half block to stand on the lower fence. This allows you to jump on top of the fence, or in the case with autojump enabled, you jump off the catwalk by accident.

If you just remove the lower fence that causes this, you can now walk as originally expected. (Object B in image).

I noticed this also happens in 1.9. So this doesn't seem to be a new issue. Just more in your face with the autojump on. (Also, I'm not turning it off. I like the new feature.)