sounds about right to me...... lace rock will also bleed ph... soaking *might* also be enough to clean the rocks, soak them for a few days and maybe even scrub them lightly with some sort of brush. boiling i'm sure would be alot better.
as a general rule, i don't think i would recommend doing this unless you have a specific use or idea and you are willing to watch the tank closely or test things previous to attempting it. you can try the vinegar test, if vinegar poured on it bubbles it will probably degrade somehow. or soak the rocks for a week or so and test the ph of the water before and after.
some scenarios, bleeding ph isn't a bad thing. alot of cichlids like the higher ph and harder waters.