Panels or other UI elements that you moved to a secondary monitor move back to the main monitor when you switch to other applications. You are using multiple monitors on Mac OS X 10.9 (Mavericks).
Solution 1: Deselect Displays Have Separate Spaces in Mission Control.
- Select the Mission Control icon in the Dock, or choose the Apple menu > System Preferences > Mission Control.
- Deselect the option Displays Have Separate Spaces.
- Log out and log back in.
For a screen shot of this dialog box, see this Apple technote.
- Command-click or right-click the application icon in the Dock.
- Go to Options.
- In the Assign To section, select either All Desktops or None.
Note: If you do not see the Assign To section in Options, it's possible that you disabled additional spaces. Create a temporary space so that you can see the Assign To options. For more information on creating spaces, see Mac 101: Using Spaces to organize your windows and applications.
Mac OS 10.9.x gives you the option to assign an application to a specific Space. The application always opens in this Space, which helps with organization and reducing screen clutter. However, all elements of that application must also exist in that same Space. The OS allows you to temporarily move elements to another screen while the application is active. However, when you switch to another Space or application and switch back, the OS assigns all elements back to the designated Space.