I use both powder and liquid down the center of the agitator, but I never, ever do cold washes. Always warm or hot, and I've never had a problem as described in the OP.
Fabric softener is another matter entirely. My FWB loves to use softener and both the cup and the top section inside the lint filter where the softener gets flung against need to be rinsed/scrubbed out after he runs a load. I don't watch over him, but I think he doesn't even dilute the stuff.