In a Dual Monitor environment or setup (monitor A and monitor B), if TOAD is running on monitor B, then all the Display Pick-List will show up in monitor A.
Other behaviors include some pop-up windows are shown behind the Toad main screen or it is not in focus. I will have to do Alt + Tab and select Toad so that the pop-up window will appear.
TOAD does not officially support Dual Monitor.
Enhancement request QCM33772 has been submitted to Development for consideration in a future release of Toad for Oracle.