At some point during larger games on hard or greater difficulty, enemy culture will spontaneously spring up (seemingly from your own planets) and start to spread uncontrollably. This will continue, undeterred by culture research or any amount of culture-spreading tech or buildings. Even if the faction that is responsible for the culture bomb is removed from the game, the culture spreads indefinitely until even capital planets fall. Once this "culture bomb" ignites, victory is essentially impossible.
Whether it is a glitch or an unintended development of a feature, this needs to be fixed. Culture should not spontaneously spark up across the galaxy and over the course of less than half an hour take over almost every planet I have in over three solar systems. Even if the Advent do have some sort of auto-culture-spread tech (which I believe they might, can't recall), this is a bit OP, and in any case, crushing the offending faction should cease all cultural influence (or at least halt it).
Fix please. Also, has anyone else noticed this?