Crawling when flying into a block (weird behaviour)

When, in creative mode, you fly into a block with a gap below (like in video), you sometimes enter crawl mode

What I expected to happen was...:
I expected to be stopped by the blocked

What actually happened was...:
I actually went into crawl mode and it's weird

Steps to Reproduce:
Just do what I did in the video (it doesn't work all the time)

If videos doesn't work, I provided 2 screenshots of the bug