Quote from Phar
First and last thing I read was "frikking". Then I realized you're obviously a newfag who doesn't have the ability to use Google Search or the Minecraft Wikipedia to see that it's a known glitch.
I began minecraft ~July 7 2011 1.7.3 Beta
My username used to be Creative_Dalek but is now Dalek since 2/4/2015
Quote from blueberry12
finally found the article about glitch after googling for about 20 minutes
.... you will only get one halfslab when destroying a double halfslab with silk touch ...