I think for as long as I've owned the Fleet Mogai its had the problem of not exploding when it dies. Not sure if this goes for the regular Mogai & Valdore or not. All it does is just rolls over (like a puppy ) and just sits there till I respawn.
My Fleet Mogai can rollover, can yours? Screenshot
If I had to guess, it seems likes it's confused between using a Singularity breach like it's supposed to and a warpcore one. This is on a FED Romulan.