The echo for setting a burst trap confuses me. This is the echo for successfully setting a trap:

You deftly begin setting a trap for the next person or group entering this place.
As you finish the setting, you load the spring mechanism with a small spear!
Ahh, perfection...
Anyone who springs the trap will be sorry!

It says plain as day that I'm setting a trap for the next person or group entering the room. Which isn't very true as far as the group goes since then this happens. All traps that are triggered are burst traps. Yet only the person who entered first gets hit with them. Not their groupmate. Bug or by design?

Target1 has arrived.
A trap is sprung!
Target1 yells 'Argh! I've sprung a trap!'
A small spear fires from the trap striking Target1.
Target1's small spear *** DEMOLISHES *** him!
Target1 staggers, nearly losing his balance.
A trap is sprung!
Target1 is surrounded by a pink outline.
A trap is sprung!
Target1 manages to avoid inhaling the noxious powder.
Target2 has arrived.

Target1 leaves.
Target2 leaves west.