Hoe durability does not decrease unless tilling soil

Samsung Galaxy S4 android 5.0.1 mcpe 0.11.1 single player survival mode.

What happened: using a new hoe in a survival game to break blocks, vegetation and kill stuff, I noticed that the durability was still mint (no green bar at all). The durability didn't appear until I tilled dirt, grass or packed dirt with the hoe. Even then the durability didn't decrease further unless I was tilling soil.

I expected: all interactions using the hoe would reduce durability.

I tested wood, stone and iron hoes and got the same bug each time.