I know this isn't the right forum, but I cannot find anywhere more pertinent, since I don't have a Windows computer from which to make a problem report.
I upgraded from OS X 10.10 to 10.11 yesterday. When I plug in my MS Natural Keyboard 4000 today, the Windows and Alt keys are no longer swapped. I looked in the Microsoft Keyboard area of the System Preferences. Keyboard Info says no MS keyboard has been
detected. I reinstalled the drivers from Microsoft-Desktop_d305.dmg, which annoyingly requires a System Restart. That made no difference.
To be clear, the keyboard is working. I'm typing this report on it. However, it's not being detected as a Microsoft Keyboard and so the Windows and Alt keys are not being swapped. I'm having to fight my muscle memory to get things done, since I expect to
find the Cmd key immediately to the left of the space bar.
The keyboard is plugged directly into a USB port on my MacBook. However, when I first plugged the keyboard in after upgrading to OS X 10.11, it was into a USB hub.