Ender chest drops itself and 8 Obsidian when mined with a silktouch pickaxe

Hello, i have Win 10 Minecraft Edition on version 1.2.3
My issue is:
Ender chest drops itself AND 8 Obsidian when mined with a silktouch pickaxe (and unbreaking III and efficiency III)
The first time it worked normally. When it was emtpy.

Regards..