Problem
Light-giving items can allow the PC to successfully 'l'ook at stuff on the floor and dungeon features that are in a darkened area. Equipping and removing one such item in the dark will trigger this.

How to reproduce it
1. Enter a dungeon.
2. Step away from the staircase, drop an item, and step away from it as well.
3. Create darkness, using the spell or scroll.
5. Equip an amulet of light or light a torch, and exit the inventory screen.
6. Unequip the amulet or torch, and exit the inventory screen.
6. 'l'ook at the tiles where you've dropped the item, or came from - you'll see them in the dark!


Notes
Walking over the things you've seen and 'l'ooking again works normally - the PC can't see anything there anymore.