OK so you're cruising at 90 inbound to a waypoint with traffic below you same direction at 70, and ATC mistakenly clear you down to 70 instead of 80
As you descend through 80 the thing goes off, you reduce descent rate or climb back to 80 and the warning stops, what do you do now?
The other traffic is still below you at 70 as only one of you should have got a climb/descent and in any event if you have manoeuvred the TCAS will still be protecting you at whatever level you have settled at.