IE9 renders differently on localhost versus qualified URL
I'm having a weird problem that I wasn't even sure how to search for an answer.
Basically, if I view my site in IE9 using a localhost URL, it renders perfectly.
But, if I view that exact same page, still running on localhost using IIS, but with the fully qualified URL, IE9 seems to ignore several CSS selectors, specifically anything that uses CSS3 like rounded corners and box shadows.
Is there a known bug/issue here that I'm missing?
Oh, I should also mention, both versions show that they are rendering in Standards Compliant mode (according to the bookmarklet I use to check).