Raid time = deafeat?

[Garanwyn]

For better or for worse, mutual kills always go to the defender.

This is a reasonable explanation as to why:

Both teams die in a raid - should be a draw?!

As you are raiding somebody else his castle and you did not win, you do not have any hero’s left to take the goods you won. So defender always wins when both teams die in the final round. I know it feels frustrating but I do not see this as a bug at all.

And, as @Kerridoc has pointed out on this subject:

Raid needs draw

Look at the bright side: it still adds 5 heroes to the Wanted chest.