Heh, there are other perfectionists here! I thought I was alone, hehe! I noticed this bug too, and it's very annoying, cause my character stepped on this trap at least 5 times, because stupid pathfinding AI doesn't moveparty members around traps. You also don't get any XP.
There is another trap that cannot be disarmed - on the Leliana special encounter (Leliana's assassins) - I said "enough is enough", checked the area in the toolset, turns out the trap is located below the ground textures, so impossible to click on it to disarm. Changed the Z-coordinate a little to move it above the ground and then Leliana could disarm it once she has detected it. Nice. XP for disarming! Probably the same bug in the Corcari Wilds.