Also happens with other invisible monsters (such as ogre magus or a goblin that drank potion of invisibility) that are then made visible with potion of visibility.

I have reported this under illogical messages, but I think it fits better as a separate issue like this.

I checked also those illogical messages before posting this, but I don't think this was reported yet (and was about to report this one there as well but realized this is a bit more complex than simply illogical message under certain situation).
If you meant (64) or (92), both those are a bit similar but still very different.
This bug is about that you can see the monster because it's visible (because potion of visibility overrides invisibility) but what generates the messages thinks you can't see it. Also if you have +SeeI, you'll see those visible invisible monsters as invisible instead of visible.


(64) Calming an invisible stalker without +SeeI: "Something appears to be rather bored.", "Something calms down." Possibly related to the bug that allows you to pickpocket them.
(92) Wishing for a monster while blind gives the following message: "Suddenly someone/something appears." A blind PC should have no way of knowing that. The same happens if you wish for an invisible stalker without +SeeI.

My thoughts also.

The entry was #50, I deleted it with a link to this issue :) The original text read:

Ok, so i couldn't see that entry because it was invisible... Or something like that.

Fixed.