Insider Review of Windows 10 reveals something weird: Microsoft seems to work on removing a good old mixer from the operating system. So far, the small menu, with its white window still resembling Windows 7, can right-click on the speaker icon in the drawer.
Fortunately, you do not have to work without the function completely. 18272 only changed context menu assignment. You can still access the old volume mixer via the Windows settings or via the "SndVol.exe" file.