There must be another variation in XFCE that makes the difference. I'm running 14.04.1 w/XFCE 4.10.1 and xfce-settings 4.11.2-1ubuntu2.
I successfully cleared the settings for changing workspaces, multiple times to even clear the default. Then I went back to the general settings page, returned to "Window Manager" and then set the workspaces to Super+1 thru 4. The settings then remained across login/outs and reboots.
There must be another variation in XFCE that makes the difference. I'm running 14.04.1 w/XFCE 4.10.1 and xfce-settings 4.11.2-1ubuntu2.
I successfully cleared the settings for changing workspaces, multiple times to even clear the default. Then I went back to the general settings page, returned to "Window Manager" and then set the workspaces to Super+1 thru 4. The settings then remained across login/outs and reboots.
HTH.
--C64Whiz