I installed an Windows Pro 8 to 8.1 Pro x64 on a desktop computer. Both were clean installations, no other software was installed. With Window 8.1 Pro, the start button worked for a day after all the updates, then booted the computer. Now, if I try to right click on the Start button with the mouse; nothing happens. Thinking it was a virus, I used Windows Defender to search to the for a virus and nothing found. No other Windows updates to fix the problem! To me it just another glitch in Windows!
I updated a laptop at the same time with Windows 8 to 8.1 X64, not the Pro version. The laptop was a OEM version of Windows 8. The laptop works fine with Windows 8.1 after upgrading it.