Player cannot jump while crawling

Summary:
A player cannot jump while crawling, unless they are near an incomplete block (even without a collision). If the crawler is in the same block/nearby to blocks such as rails, buttons, carpets, iron bars, etc. he can jump.

Steps to reproduce:

1. Crawl in a space 1 block high.

2. Try to jump.

3. Place a button underneath.

4. Try to jump.

Observed results:
You cannot jump while crawling except in certain scenarios.

Expected results:
You can jump while crawling.

Video: