The game saved just after the bug occurred, frustratingly, but I can provide an annotated screenshot of the aftermath.
The order of events leading up to the screenshot, all of which happened in a single turn, is as follows:
- UFO door is opened by the leftmost crouched Xenonaut, revealing two Caesans (circled).
- Machine-gunner opens fire into the centre of the UFO, between the two Caesans.
- Both Caesans are marked as 'suppressed' by the game.
- The Caesan circled in green is indeed suppressed and behaves normaly.
- The Caesan circled in red takes a reaction shot as soon as the machine-gunner stops firing, killing him.