Odd silk touch duplication glitch

Me and my sister were playing MC and messing around. I decided to place a furnace and break it while messing around and the only pickaxe I had was a silk touch pickaxe, weird thing is we got a second furnace from it. So we tested a few things and found that if you broke these items with a "Silk touch" item it would give you a second one. When we did it with the banners we also ended up getting a item called "Banner", and while in hand it had the texture of a sign.