Thank you for your reply. Actually, the wheels are in motion already. Our contractor (who installed the door) called the showroom, who called Glasscrafters. They are fabricating a new door for us. Are you saying that it is not safe to use in the meantime? The showroom guy said we should just put a piece of tape over it so that we don't accidentally touch it, but that otherwise we can use the shower.

Plumbing flux is causing "mold"? That is a first. During construction a house can get dusty from construction. Add to that the fact that mold spores are pretty much everywhere. You could have had spores and a light coating of construction dust on the surfaces in your bathroom. Add moisture from using the new bathroom, and you can get a bloom. But after cleaning and use, it should all go away. You wrote you have a "mildew proof tile" so I'm guessing it's a glazed ceramic? Do you have any photos of the "mold?" Now lets set the mold aside for a bit and move on to this being more if a water imbalance. If water is allowed to sit undisturbed in new copper plumbing, sometimes you can get a chemical reaction between the water and the new copper. It doesn't happen all the time, it does depend on the composition of the water. The precipitate that is formed can adhere to the inner walls of the copper tubing. When the plumbing is then used, the precipitate can slowly flake away as water flows through the new plumbing, it can stain fixtures or tiled/grouted surfaces. That staining usually does decrease and disappear over time as the interior lining of the plumbing gets scoured clean with use. Mold is one thing. It can form anywhere, even away from areas that get wet from direct water spray, because it's an "environmental thing". Mold spores plus a moist environment can give you mold or mildew, even away from where water hits a surface. Stains from dissolved or precipitated minerals is another. They usually form where the water directly hits a surface, or where standing water occurs. On a plumbing fixture, or at the base of a wall where the floor slope may not drain well, or around a drain, for example. So take a good look and see if it's a mold growth or a mineral stain. Mold should come off with a soft scrub cleaning. A mineral stain may not. You could also have your water tested, especially if you're on your own well. If you have any water treatment in your house, you could have the settings on that checked as well. Good luck!

Thanks Jerry for the link and how to repair a tile. I hope my tiles do not chip when they are finally installed.

Looks like bullnose on an outside corner? Tough to say what would structurally stress an area like that. A shower rod? Good news, it's on the edge of the installation. Removal and repair would not be difficult. And the location minimizes the effective compromising of any waterproofing membrane that might be underneath. Often times cracking of tile occurs on joints. Joints in framing. When new framing settles, or where new framing meets old. Differential movement within the wall. Near the top corner of an exterior window, etc.