Apparantly yes, it is a thing. Way I read the description was that rocks have spots on there structures where they will absorb alk until those "holes" in the crystal structures are filled/bonded with alk. Until they get filled they absorb alk from the water. Once they are filled, they will continue to lose and gain alk but at a rate of equilibrium with dissolving and absorbing it. I have not tested this, but the guy who posted it isn't a slouch chemist (or geologist) like myself. Other people have reported the same thing, always new dry rock.
I tossed a dry chunk fresh from the lfs and measured a few ppb of phosphorus being released from fresh-dry quarry rock, but I haven't tested alk. I did start adding baking soda to my rock tanks (for curing and storage) when I realized that alk is absorbed by these rocks. I'd rather have a rock leaching extra alk instead of your situation when I add it to a system. I have also added lanthanium chloride into the barrels if I measure P in the water, and keep adding until I get zeros. Then I rinse out the buckets and soak them in fresh salt water so they are ready when needed. hth.
