The distinction I was making (which I think most got) is that with the engine room, you have already used the action. Thus, the action being available afterwards does not effect it already having been taken (wow, that like time traveler speak).
When moving… you discard BEFORE you move. So the sabotage occurs before and could take a location out of service.
Thus, my Roslin "discard two card to activate a location" - her discard would be BEFORE the location "action" as used.
With engine room, the action is already taken, then it would be out of comission, so the action completes.
But don't you discard a card to catch a transport to another ship? So at the end of your movement phase, which is powered by the discard, you arrive at a damaged location.
When you discard to activate the engine room, you could use a similar logic. You discard a card to activate the engine room. But at the end of the action, the engine room is damaged, so it doesn't work. At the time you were fueling the engine room, it seemed to work, but upon completion it didn't. Similar to what happens with ship to ship movement. You took a ship to a location that you thought was functional, but it turns out it wasn't. Both ship to ship movement and the engine room are options being powered by the discards.
Now I also do see the argument that you spent the cards to perform the action so the action takes place, but then there is a big mishap in the engine room.
So I don't see a clear cut answer here and have a feeling there isn't one unless someone official speaks up about it.
With Roslyn, I am trying to remember how her disadvantage is worded. But I'm more inclined to say that there is two steps here. First step she discards to activate a location. Second step she activates the location. Which would put her in sick bay and she wouldn't do the actual engine room activation. But I don't recall that being clarified anywhere either.