It happened to me too once. I had two Skellens on board ( I copied the one with Letho: Kingslayer). I played Coehoorn into Garrison, then I used one Skellen to replay Garrison and used it to buff my second Skellen. But right after I buffed him, his order disappeared and I couldn't use it to replay Garrison a third time. It cost me the game too.
I keep thinking that the act of buffing him glitched out his order somehow.