Simple enough, with Haste (I've also tried resistance, it does the same) you clearly break blocks very quickly, but when you leave the world and rejoin (ignore the fact that i went into video settings) it resets the level of haste.
Edit: Uploaded correct video file
Related issues
Attachments
Comments
migrated
[media]
migrated
That's not really a duplicate but marked as "won't fix" regarding over-leveled things so fair enough.