I also hit this in 0.17.5: removed several purple techs and refilled the queue with lower tier research. Game crashed as soon as I hit 'T' to exit the research screen. Logs attached in case more data is helpful.

When an underground pipe contains a fluid, and the "to ground" side is adjacent to a pipe that is part of an empty fluid system assigned to a different fluid, reversing the underground pipe causes the new fluid to override the old one. To demonstrate the issue and why this is a problem, se...