Interesting description for this update in the Windows update screen - totally different to Microsoft's KB page. This is on my laptop which didn't have the update installed yet:
After the update claimed it was installed, I didn't see a 'GWX' folder in system32, so I searched the OS drive for it. In the short time it took the command prompt to search the drive, it suddenly appeared:
When I brought up the task manager, I could see a Windows installer process running hogging the CPU for another minute. So this update is quite sneaky, continuing to run despite the Windows Update screen claiming the update has already completed!
It's similar to the pesky .NET framework updates where they hog the CPU compiling modules in the background for several minutes after Windows Update claims it finished installing them.