Discovered this while running a mass replay test of LPO2 to test impact of Nepster's latests changes.
LPO2's zombie levels were all coming up as "undetermined", as were a few others. I had grouped them in initially with "replays broken either by Nepster's changes or my recent Fencer changes". Testing them purely on Nepster's changes, they were still broken. However, I decided to go a step further and test them on the stable version - and indeed, even here it reported them as undetermined. I tested the most complicated one manually and it passed, leading me to believe this is an issue with the replay checker, not the replays or NL's physics.
The issue appears to be a result of the replay tester not even receiving the "game has finished" message for some reason. This is weird, because regular gameplay interface receives it perfectly fine. Additionally, it does not matter whether all zombies are still alive at the end of the test, all are dead, or somewhere inbetween - the same result occurs.
Found and fixed the cause of this.