I feel it is necessary to bump this bug report up again, because:
1. It's a pretty significant bug.
2. Nobody seems to have done anything about it.
3. I am repeatedly getting pestered about issues with Tortured Planet that arise specifically from this bug.
Let me clarify what the actual problem is. This isn't an issue with teleporters, this is an issue with Trigger Each Time. Linedef executors activated through an Each Time Trigger will fail to work for any player of Node 2 or higher.
For teleporters, this isn't really a problem, because it's better to use Continuous triggers for them anyway. But there are some kinds of effects that only work properly with Each Time triggers, including several effects in the later levels of Tortured Planet. These effects break in Coop, and reconfiguring them using Continuous triggers would be unfairly complicated (they would need to be applied to an Intangible, Invisible FOF, and call sector movers to drop the ceiling of the FOF once before the effect starts and raise it again after it's over). I mean, that would circumvent the problem, but isn't that why we HAVE an Each Time trigger? So that we don't need to do all that?
So...yeah, this problem should really be looked at more closely. It's quite annoying.