There's a whole bunch of "holy crap" listed there.
Sorry you were the last to touch it so hopefully you don't own it now. Try a grout colorant as it will seal the grout with an epoxy overlay. Maybe that will keep drywall satan from rearing his ugly head....for a while.
http://www.custombuildingproducts.com/products/aqua-mix/grout-colorant/aqua-mix-grout-colorant.aspx