The bug:

Holding left click on an obsidian block with end crystals and placing the end crystals does not work. This makes left clicking then right clicking immediately to place the end crystal not work. It also ruins the placing and breaking speeds of a Crystal PvPer when they're trying to do so with crystals.

Steps to reproduce:

1. Place an obsidian
2. While holding an end crystal, hold left click then try to right click and see how the end crystal doesn't place on the obsidian

Video:

Here's a video showing the bug:

https://youtu.be/klJSOB3w-uI