Some records do have a " dirty pitch shift " in them which makes them a bitch to mix. Also if the pitch controll on the decks is a bit warn or dirty the the pitch will slide a bit sometimes.
The reason the beat did not go out when you had the quarts lock on both decks is because it was locked. When you move the pitch sliders away from the center ( the lock position ) you are relying on the variable resistors in the slider which can be a bit iffy on some desks. One of the places I play they have some realy old 1210s which have been played hard and they were a night mare to mix on untill I confinced the owner to get the pitch controll replaced.
On a side note - - If you do have a record with a pitch shift in it towards the end. It is a real laff the play it as you hand over to somone else in a back to back battle
