if martin doesn't respond here I think you might be able to e-mail him. I haven't looked into what is happening chemically when you put lactic acid in your water. I remain mostly blissfully ignorant beyond the level of "do this to bring pH down!" works here 
You and I both. 
The reason I even posed the question earlier is, my starting Ca levels are fairly low, and for my pale beers, knocking the CO3 down is a must. However, for my dark beers, like my most recent stout, I actually forgot to add any calcium to the mash, and just used my tap water straight up (filtered, but no other additions).
Tasting the wort during runoff showed that I must've had good conversion (wort tasted malty and roasty), and visually, the beer is clear (when held up to a strong light). Tastes good as poured.
I know the CO3 is being neutralized to some extent, either through reacting w/ lactic acid in a pale mash, or with the acidity of dark-roasted grains in a dark mash.
So, this got me thinking that perhaps the Ca that was originally bound to the CO3 was somehow freed up to aid in mash conversion/yeast flocc'ing, etc.
I could be wrong.