these ports are not modified in any way by the mod, so its probably some sort of edge case vanilla bug you ran into

Man this is so annoying, i hate it that it happens so often but not always.
And thank you for checking anyway.

I'm seeing this issue as well, particularly with radbolt rockets (Never seems to be an issue with petroleum rockets). Rockets that were formerly petrol rockets that I converted into radbolt ones (without changing the starfarer module interior) all start hitting this.

I've been pre-emptively triggering the issue by setting up plumber-empty commands on the pipes at the input port inside the rocket just after launching my rockets and mopping the resulting water, but it's causing knock-on effects with the sudden introduction of a large amount of heat into the capsule, etc.

It seems to me like there's a couple of packets of liquid buffered by the liquid input ports in the capsule itself, and that liquid is what's getting super-heated somehow. I know you mention not having modified this code, but I'm wondering if there's some indication that the ports have some kind of buffer that's always had this bug? I never used to hit this issue until I started using Rocketry Expanded, so I'm wondering if there's some kind of race condition that's been exposed.

I'm running Rocketry Expanded with most of the options turned off except for automation relay satellites and the port ladder and insulated wall adapters.

I am also having this issue. Getting real tired of finding my cabins overpressured because a pipe broke and there's water covering the vent.

Yeah, encounter this as well. It is relativly annoing, because I use almost exclusivly Radbolt Rockets.