Adding to the rest of the feedback, and hoping the bug is quickly fixed considering how awesome the game is otherwise:
Had the same problem completely blocking two of my games at the verge of victory. Each time a lonely planet (two different races - Thoraxians and Burlusts) is against the whole galaxy, without any space forces, largely beaten in terms of ground forces (Burlusts went down to 1M Pop, Thoraxians still managed to grow but were severely outnumbered).
Saves of both situations included.