losing an 8-4 lead is completely normal because games are 2 halves
if defenders go 8-4 on 1 half
defenders should also go 8-4 on the other half
losing a 12-8 game is not normal though
none of it is a curse, just bullshit gamblors hope for. It's either a defense or attacker sided map or you have teams that do better on a specific side.
e.g. Na'Vi just pops off on any attack side, no matter if they're 10-2 down on defense