Improved invis weirdness

Improved invis acts *very* oddly sometimes when you change your held item: I had some mobs tracking me that were too low level to see past improved invis. I held a talisman (instead of an artifact) and suddenly, all the mobs attacked me as if they could see me. After fleeing, they couldn't re-initiate, as usual. Here's a snippet: You stop using a silver-bound tome. You hold a warm topaz shard in your hands. A minotaur slave yells '! Nnoow yoou die!' A minotaur slave's beating wounds you. A minotaur slave yells '! Nnoow yoou die!' You drive a minotaur slave's beating back with your connecting blow. You parry a minotaur slave's beating. You parry a minotaur slave's beating. A minotaur slave has some small but disgusting cuts. Note that I didn't "fade into existence" in any manner there.