To reproduce:

1. make the setup as in the video
2. enable autojump
3. walk against the block under the amethyst bud (as in the video)
4.  you don't jump
5. press space
6.  you can jump

In this report, with amethyst bud I mean the ones where you get shards from and not the blocks.

I would expest that autojump still jumps when you're at the side on which the amethyst bud isn't placed, but it doesn't. It seems that autojump sees amethyst buds as full block over their complete width.