Taurus titanium Ultra-Light model 85

I recently purchased a .38 ultra-light titanium, and after putting 50 rounds of Winchester factory ammo through it, I noticed that on the bottom side of the top strap, just above the chamber, the blueing was worn off. At first, I thought that it had been scratched off, but there's nothing in the action that could cause this. Was it caused by the heat\chemical reaction from routine shooting? There are no other signs of wear. The space where the blueing is gone is bright and shiny. What could possibly cause this? I have never seen this occur on any revolver I own (which is quite a few) but this is the only titanium gun that I own. Sorry, I don't have the capabilities to post pics. Any ideas?

Peace and God bless, Wolfsong.