This is probably the 3rd time I've posted this bug over the last 10 years, but I don't think it was ever addressed or even responded to previously.

Basically if you have a ranger and scan, you can see things you can't normally see like hidden assassins or invisible mages. But when you go into the room, you cannot see them.

I know for sure this is an issue with explorer rangers, although I vaguely remember it happening with other types as well. Here's an example:

You scan north.
***** Range 1 *****
(Invis) A sturdy gnome stands by the riverbank, glaring at a log.

walking north

You step out from your cover.
A Cleared Area in the Feanwyyn Weald
Most of the trees and underbrush that once filled this part of the forest
have been cleared away, most likely the work of axes and saws to judge by the
appearance of the various stumps that still dot the land. The area around
you is filled with activity, lumberjacks moving to and fro with purpose, axes
slung proudly over their shoulders as they carry on with their various tasks.
The river runs close to the northeast, a shallow bank of loose gravel
providing an easy place to prepare the logs for their journey to Galadon. A
weak breeze stirs the air, carrying with it the faint scent of burning brush,
as well as the sounds of a busy camp.

Exits: north east south west

No gnome here!

Explorers have a bonus to seeing upcoming danger, but not necessarily seeing it in room with them.