This window has a "dock" type (_NET_WM_WINDOW_TYPE_DOCK), therefore is
ignored by Cairo-Dock.
I don't know why the devs have decided to make the Dash window a dock
(there is certainly a reason), but what's sure is that you can never
access Cairo-Dock if the Dash is opened (because they are both dock
windows and the Dash window appears after Cairo-Dock).

2012/6/30 MC Return <email address hidden>:
> matttbe, here the output:
>
>
> sleep 5 && xwininfo && xprop
>
> xwininfo: Please select the window about which you
>          would like information by clicking the
>          mouse in that window.
>
> xwininfo: Window id: 0x420000e "unity-dash"
>
>  Absolute upper-left X:  64
>  Absolute upper-left Y:  24
>  Relative upper-left X:  0
>  Relative upper-left Y:  0
>  Width: 1856
>  Height: 1176
>  Depth: 24
>  Visual: 0x21
>  Visual Class: TrueColor
>  Border width: 0
>  Class: InputOutput
>  Colormap: 0x20 (installed)
>  Bit Gravity State: ForgetGravity
>  Window Gravity State: NorthWestGravity
>  Backing Store State: NotUseful
>  Save Under State: no
>  Map State: IsViewable
>  Override Redirect State: no
>  Corners:  +64+24  -1280+24  -1280-0  +64-0
>  -geometry 1856x1176+64-0
>
> _NET_WM_ICON_GEOMETRY(CARDINAL) = 8, 1067, 48, 48
> XKLAVIER_STATE(INTEGER) = 0, 0
> WM_STATE(WM_STATE):
>                window state: Normal
>                icon window: 0x0
> _NET_WM_DESKTOP(CARDINAL) = 0
> _NET_FRAME_EXTENTS(CARDINAL) = 0, 0, 0, 0
> _NET_WM_ALLOWED_ACTIONS(ATOM) = _NET_WM_ACTION_ABOVE, _NET_WM_ACTION_BELOW
> XdndAware(ATOM) = BITMAP
> WM_PROTOCOLS(ATOM): protocols  WM_TAKE_FOCUS
> WM_HINTS(WM_HINTS):
>                Client accepts input or input focus: False
> WM_NAME(STRING) = "unity-dash"
> _NET_WM_WINDOW_TYPE(ATOM) = _NET_WM_WINDOW_TYPE_DOCK
> _NET_WM_STATE(ATOM) = _NET_WM_STATE_STICKY, _NET_WM_STATE_SKIP_TASKBAR, _NET_WM_STATE_SKIP_PAGER
>
>
> ** Changed in: cairo-dock (Ubuntu)
>       Status: Incomplete => New
>
> ** Changed in: unity
>       Status: Incomplete => New
>
> --
> You received this bug notification because you are a member of Cairo-
> Dock Team, which is subscribed to cairo-dock in Ubuntu.
> https://bugs.launchpad.net/bugs/1017550
>
> Title:
>  Unity Dash: The Dash does not get recognized by docks like Docky,
>  Cairo Dock or Plank when set to fullscreen and the docks do not
>  autohide
>
> Status in Unity:
>  New
> Status in “cairo-dock” package in Ubuntu:
>  New
> Status in “docky” package in Ubuntu:
>  New
>
> Bug description:
>  In the case of Docky the situation is even worse, because Docky stays above the Unity Dash, so selecting lenses with the mouse becomes impossible.
>  Tests with Cairo Dock 3.0 and Plank showed that they just do not window dodge or autohide if the Dash gets maximized, so the Dash & lenses are on top of those docks then, but they do also not autohide like they should.
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/unity/+bug/1017550/+subscriptions
>
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