A trapped floor square will be shown as a dark square until the trap is detected. After that, the square will display the graphic for the appropriate trap. Because of this bug the location of all undiscovered floor traps is known to the player before they are discovered.

If an item lying on the trap square is kicked away, the square will still display the item graphic until the screen is redrawn. The same thing happens with trap/spell effects and with the character graphic itself when it steps on it (see screenshots), as well as with monster graphics.