A little salt also can help when it gets "off". Thanks to Leahs Mom for teaching me that! (just want to give credit where credit is due!)Yes that has happened to me as well. Seems like nothing a few capfuls of ACV doesn't cure, like you said.
I am interested to see what happens as things warm up (if they ever do!) b/c I've had no issues all winter but it was the warm summer months that it got off- yeast growing on the top, smelling wrong and attracting flies and fruit flies like crazy. I am keeping it inside this year to see if that helps.