My two ship fleet attacked a single Drengin ship defending its home world. The confirm battle window that comes up before the battle viewer showed this, with what looks like 32 bit overflow values for attack/defense/hitpoints:
Sorry to keep posting minor problems like this, but on my system I can't get the game to crash 
Edit: I have a saved game that demonstrates the problem. Just use the fleet next to Drengi (in the upper right of the map) to attack the planet and its defending ship.