A workaround in windows 10 (the issue was not before anniversary update) is activating the "Auto hide in desktop mode" function. Right-click on task bar and open the configuration window to see the option.
Check this: http://www.tenforums.com/general-support/61190-how-do-i-disable-always-top-taskbar.html
In other place I found one posible explanation for your "compatibility" workaround: http://answers.microsoft.com/en-us/windows/forum/windows_10-start/windows-10-taskbar-always-on-top-would-like-to/a39fe424-44f1-457e-8669-9f9f33e9e7e7
The taskbar option "Always on top" and the ability to disable it, that was in windows versions through windows vista, was removed from windows in 7, 8, 8.1 and still has not been restored with windows 10. I personally have made more than request to have this functionality restored