Summary:
Crawl mode is activated when you sneak and jump onto the bed. If there is a block above you at the moment of jumping, you will be completely crawling, otherwise you will be crawling for a moment, and then you will be pushed out by the blocks. In versions 1.20.73 and below the player starts crawling without jumping - see MCPE-178370.

Steps to reproduce:

1. Place the bed.
2. Place a full block 1 block above the bed and you.
3. Sneak.
4. Walk close to the bed and jump.

Observed results:
The player starts to crawl when jumping.

Expected results:
The player does not start crawling when jumping.

Video:
0422.mp4