Duplication mining Furnace with Silk Touch Pickaxe

Phone - Android - Huawei Nexus 6P

Having placed a freshly crafted furnace in the wrong direction, I mined it again with a pickaxe (only had Silk Touch at the moment) so that I could correct it's rotation. Suddenly I noticed that I had not one, but two in my hotbar. A quick test (placing a furnace and mining it again and again) confirmed that an extra furnace dropped each time. Now I know that silk touch is special, but I don't believe this is supposed to happen.

Pickaxe details:
Type: diamond
Enchantments:

• Unbreaking III
• Silk Touch I

It seems like only the furnace is affected; mining stone or anvils drops one item. Didn't test on other blocks.