Effects with amplifiers over 4 (level V)/enchantments with level over max default value are not supported
While under the effects of Mining Fatigue 5 or higher, it becomes impossible to break anything. Even with Haste 100 and Eff 100 you still can't even break tall grass.
[Mojang] Jeb (Jens Bergensten) added a comment - 04/Mar/13 11:22 AM
I dunno why Dinnerbone removed the limit to the effect command I don't want to chase "bugs" like these..