Today I noticed that when viewing the move relearner screen (the one where you are shown a list of moves that a selected pokemon can relearn), a command window is shown off the side of the screen. It is only visible when the game is in fullscreen, as it was likely moved outside of the main window to hide the interface.
It doesn't impact the performance in any way, it's just obviously not intended. This issue can be solved simply by adding the line @sprites["commands"].visible = false to the script section PScreen_MoveRelearner at line 73.
I have confirmed that this exists in vanilla Essentials.