It actually blew up four things. In both of the replays people have provided, it seems to be working as expected, and then working as expected a second time for free.
Ah yes. Sorry, I didn't keep watching after the first 3 were discarded.
You're right, the effect is getting carried out twice. Looking at the Gemp-Lotr code, it appears to be because the effect happens once for each exertion (so twice in this case) instead of just once. This will need to be fixed.