yes iknow this. i spent a lot of time trying to figure out why everythig there was so inconsistant. maybe somehow my difficulty level was messing up. i thought i started every game on hard. but one time the guy in the party disarmed all of them(25). next time he did the ones you speak of. the next time he dont even recognize they are traps hehehee
edit: OOOPPPS i wasnt sneaking. they show up. but still the first time was -1, +10, +10 xp and they all were disarmable