Currently ObjectDock's special WindowsKey+D (Show Desktop) handling, which prevents it from being hidden by the "Show Desktop" windows command, is only set to kick in for "Always on Bottom" and "Always on Top" modes.
For the next release, I'm considering changing this so that the "Keep visible during a WinKey+D/Show Desktop" ability does its thing regardless of if its on top or not or whatever. My logic, you can always disable it like you could before from the Advanced/Misc options (however not on a per-dock basis), so pretty much only functionality is gained. The only way you lose out in any way is if you had OD+ and have several docks...and some docks you want hidden and others you don't during a WinKey+D.
Any protests?
-Jeff Bargmann
ObjectDock Lead Developer