Mining fatigue level 4 behaves like mining fatigue 5+

Without Mining fatigue level four I'm able to break blocks as normal, however with mining fatigue level 4, which according to the wiki ( http://minecraft.gamepedia.com/Effect ) is an 80% speed reduction, I am unable to break blocks.

This appears to be also apparent with level 3 and 2, but I have not tested them fully.

Video: http://youtu.be/iQsBT2bPHlU