I also had this problem, and I personally did not like the hack proposed at the associated bug report by user Fabounet (cf. UBod's answer), mainly because it means you have to apply the hack again and again each time you update Cairo dock.
I came up with a (in my opinion) cleaner workaround, which I also posted at the bug report. It basically involves adding another item to the panel which also has Shutdown/Logout/Suspend/Restart functionality:
Hold down Super+Alt, right click on the Gnome panel, and click on Add to Panel... in the menu that pops up.
In the drop-down list that appears, look for the item User menu (described as Menu to change your settings and online status), select it, and click Add.
This will add a user menu to your panel. It shows as an item displaying your name with a speech bubble beside it.
The nifty thing is that this item also got menu points for Switch user, Log out and Power off (the latter of which lets you choose between Supend, Restart and Shutdown), and these work, as opposed to the same entries of the "default" gear-wheel item in the upper right corner of the panel.