I seem to have discovered a flaw in DO 11, quite accidentally TBH. I created a floating toolbar, chose for it not to be on top, which should effectively make it visible when navigating to desktop, but when I use the Alt+Tab combination to go there, the toolbar disappears! When I minimize all the windows to show desktop, it stays though.
If you alt-tab to the desktop, the desktop goes on top of all windows, except those which are always-on-top, or which are docked to the desktop's edges.
Correction: Including those docked to its edges, if they are not always-on-top. This is something Windows does, not something Opus is doing itself.