When left clicking with a diamond helmet in hand, the game crashes.
I found out that when you left click armor, you are putting it on.
When I went to left click with the helmet in my hand, the game crashed.
1. In creative mode press the inventory key. (Default 'e'.)
2. Grab a helmet.
3. Put the helmet in your hand.
4. Left click.
At the end of the video, my recording software stopped because the game crashed, and Java was no longer in charge.