dash doesn't activate when there is no root window

After disabling the desktop icons, as I usually do, with
gsettings set org.gnome.desktop.background show-desktop-icons false
the dash no longer appears (either when the meta - or is it super? - key is pressed or by clicking the dash icon) if no window has focus (i.e., if I minimize all windows or or move to an empty desktop).
Also, the menu from a minimized window may be 'left behind', sometimes in an unresponsive state; and in that case the dash will appear (not sure if it always works). In some cases, the dash appeared but failed to register input, passing mouse over events and at least some keypresses to the underlying windows.
This behaviour is reproducible, and it is reverted by re-enabling the desktop icons.

I am running 12.04 with all recent updates. Package unity is version 5.14.0-0ubuntu1.