aka - hidden block glitch?
note: This glitch is not the same as the totally not rare "blocks reappearing after broken glitch"

When destroying blocks at a high rate (nether rack with an efficiency V pick for example). Some blocks don't break properly and a weird completely invisible glitchy hitbox (which make your character spaz out when walking into them) remains. Which whatever I do (even after first placing a block in it and then destroying it) does not disappear. After reloading the safe file all these anomalies are replaced by the nether rack that used to be there and act normally again.

edit: "Which whatever I do (even after first placing a block in it and then destroying it) does not disappear." = false

edit: also doesn't drop item