I think it's one of StartIsBack's features Try the demo its free for 30 days with no nags and the license only costs $2 USD and they don't impose a limit on how many times you can activate it as long as it's on the same PC unlike other apps like Start8, activate it 5 times and your key is blacklisted It also has a lot of features in the options such as enabling animations for the start menu and stuff
windows 8.1 rtm requires the startisback + version which you have to look for on there home page sorry didn't look close enough my bad