Not that I don't believe you but I'm having a hard time with it just being one full row around the shower.
How is the lighting?
Can you take a picture or two?
If it is just one row then I doubt it will stay that way, it should spread. Now if it was at the bottom of the floor or something but eye level?
I have seen a lot of weird stuff and this would rank up there with weird. It will be interesting to see if the problem expands to other tiles........
If you can take some pictures and post them, I will forward them to a guru who might be able to tell me what is going on.