i Took a look at this. Couldn't find any sore thumbs in the code, but I noticed that the sectoid (navigator) has only 7 tu in the .Sav, so am wondering how it could do 2 reactionshots.
It appears the sectoid got temporarily stuck in a phase or mid-state, with the shots lined up and ready, because all it takes is moving the tank to invoke those shots and get them out of the queue (so to speak) and if the stun is then performed it goes ahead normally,
and it strikes me that this had to be written in the .Sav ( but couldn't find anything too unusual there either - just the 7tu )
[ more: ] somehow the sectoid got stuck in STATUS_TURNING, instead of STATUS_STANDING, which *is* written to the .Sav; note how it still has its weapon raised. Ie, changing "3" to "0" in the file fixes/worksaround...