In Underground and Terminal we have that part of the map, when - after blowing up the first objective - your respawn point may move for the last time. But I still don’t get how it’s working.
Let’s take Underground as an example. Attackers blew up the fan controls, and their spawn moved right next to its remains. We were pressing them at the bottom of escalators for about a minute, but then, suddenly they didn’t come at us, not even one. They respawned below second escalators, in their final spawn, and just went for the second objective 
It’s the same in Terminal - how many times were you defending building behind the wall only to find yourself fighting newly respawned enemy team with spawnprotection, because their spawn moved there without any reason?
Can someone explain to me the mechanics behind this?