DY-Ehas isolated the reason why Fast User Switching may not correctly redraw the desktop wallpaper and dock when it is done on Mavericks.
Killing the Dock Application with the Applications -> Utilities -> Terminal appears to fix it.
followed by return key within the Terminal will force the Dock to reboot.
The issue appears to be most apparent on larger desktop screens than on Notebooks.
Fast User Switching is the ability to add a User menu in the upper right with your Apple menu -> Systems Preferences -> Users and Groups -> Login Options.
It allows people to have multiple logins on their computer running multiple processes concurrently.