Hey guys,
Most spray bottles should hold up to Star San. The toughest thing about it is phosphoric which, in the realm of strong acids, isn't too bad. I think what may be happening is that the Star San is complexing with dissolved solids in the water (generally hardness, but can also be magnesium, iron, manganese, etc.).
This has a bit to do with why we introduced San Step-- it doesn't complex with water minerals and won't clog spray bottles. I don't want to get overly commercial, so I'll leave it at that and ask you guys to contact me if you're interested in hearing more about it (and we'll be at the Homebrew Con if you want to come by and see our demo-- we're partnering with CM Becker/Keg Connection for distribution).
Hope that helps,
Rick Theiner
LOGIC, Inc.