With the switch from Snow Leopard to Lion, some users have reported a peculiarity in the way OS X handles multiple workspaces. (Those virtual desktops were managed by Spaces in Snow Leopard, by Mission Control in Lion): If you try to assign a given app to a specific Mission Control workspace, that assignment doesn’t always stick. And if you try to tell an app to appear in every workspace, that may not stick, either. If you’ve been experiencing this sticking problem, an anonymous Hints reader found a workaround solution.
Typically, you assign an app to a specific workplace in OS X Lion either by dragging it from one workspace to another in Mission Control or by going to the workspace you want, opening the app there, then right-clicking on the app’s Dock Icon and selecting This Desktop from the Options menu. To assign an app to every workspace, you need to go to that same Dock icon menu and select All Desktops instead.
If those assignments aren’t sticking, try switching them around: In other words, if you’ve tried to assign a given app to one specific workspace, go to the Dock icon and select All Desktops instead. Close the menu, then open it back up and select This Desktop. In the same way, if you want an app to appear in all desktops, go the Dock icon menu, select This Desktop, close the menu, open it up again, and select All Desktops. Toggling those selections may make the app behave the way you want it to.