Splitscreen button in Windows 10 edition

Note: The affected version is just a guess, because this was encountered by someone else: https://gaming.stackexchange.com/questions/325168/minecraft-windows-10-edition-splitscreen
I don't have Windows 10 edition myself.

Windows 10 edition has a button for splitscreen, like on consoles, but it does nothing. The button should get removed or splitscreen implemented.