I open the window menu on the panel and right click on a window title, This bring up a menu with option like move, resize, and move to othe workspace. But when I try to move a window to another workspace, nothing happens. Other buttons on that panel, such as maximize, do work. Fedora with xfce4-panel-4.12.0-4.fc23.x86_64
Same here with xfce-base/xfce4-panel-4.12.0-r1 on Gentoo. The "Move to Another workspace" only works on the "Window Buttons" panel item, but not on the "Window Menu" panel item. The Component is actually named "Window Buttons", not "Windows Buttons", and should be renamed in bugzilla. Moreover it would be useful to have a context item like "Move to current Workspace" as this is the most obvious action for Window buttons beside switching to the other window on the other workspace.
Works for me with 4.14