Now Windows 8.1 RTM is available via Technet and MSDN it is installed by several ITpro’s. And then it is just a matter of time befor someone finds an issue. This because the code of Exchange doesnt recognize Internet Explorer 11 correctly and this will result in OWA to be displayed in light mode. As you may know OWA light doesn’t connect all the options which are available in the full blown OWA. Microsoft will probably fix this in a future update so you can use Internet Explorer 11 in full blown mode. This is confirmed by something I discovered when using Office 365. It looks like my tenant is already upgraded because Interne Explorer 11 works OK for me. The on-premise environments will need to wait till Microsoft releases an update which contains the correct code to recognize Internet Explorer 11.