Inexplicable Horror Marking

[markmayhugh]

Recently in my current game of Dominion 3, I had my Pretender and one of my heroes get inexplicably horror marked.

With my Pretender, he was horror marked the same turn he searched and found The Demon Gate. According to the database, the Demon Gate is not supposed to horror mark.

As for items, according to the database, the only items that are supposed to horror mark are the Lightless Lantern, the Tomb of High Power, and The Forbidden Light, and they did not have these.

My Pretender has not been involved in any battles. My Hero was involved in a battle right before he was horror marked, but I watched the battle carefully and the Hero was not horror marked at the end of the battle.

As a new player, I really want to understand this. Is dom3_db trustworthy with respect to horror marking? Is it possible that searching and finding the Demon Gate horror marked my Pretender? Is it possible that something else they are carrying like the Ankh or Robe of the Magi or Picus's Axe of Rulership or Procas's Axe of Rulership could horror mark them?

Thanks in advance for any insights you can offer!