Obsidians aren't grouped together in Creative

The bug

Despite obsidian and crying obsidian being obsidians they are not grouped together in the creative inventory.

How to reproduce

1. Open the creative inventory and navigate to the Building Blocks tab
2. Scroll down until you find obsidian
   Crying obsidian is far below it, instead of next to it

Expected behavior

Crying obsidian would be grouped with and shown next to obsidian in the creative inventory.