I've had the same problem with several older bottles of vallejo washes. The new formula does not have the problem.
For me, the issue only occurred when I diluted the washes with water though (regular tap water, which in my part of the world is actually purer than bottled mineral water. yes; we're blessed...
). When used straight, the washes did not white over at all.
I also have two large 200 ml screw lid pots/jars of vallejo washes (black & sepia, old formula), but those have never whited out on me, even when diluted...
I've switched to the new formula for almost all washes by now, and when buying new ones, I always check to see if they're the new formula, just to be sure. However; there'll be a time when they will take the orange 'New Formula' indication off theit labels, and then it'll be impossible to see whether you have a new bottle or some old stock with the old formula.
In that case, I suggest testing the washes before applying them to anything valuable...