Sometimes, my player avatar goes into crawling mode, even though they shouldn't.
When playing, you could be mining a tree, usually your avatar doesn't think to start crawling, and so; they shouldn't.

What instead happens, is the avatar sometimes starts crawling, I don't know why, but I do know that it didn't happened before snapshot version 20w06a.

To try and recreate it:
1. In either creative or survival, walk into a full block, whether that block is translucent, semi-translucent or completely solid.

Sometimes, it will put the player avatar into crawl mode, this may not occur often, but, it has happened to me so many times, that I just had to say something about it.