[jsty]

I'm on the side of the original wording here as far as correctness is concerned - "has proven to be" is a common expression for "in our experience, it is", whereas "has been proven to be" would give the connotations of formal proof.

This is just one of those quirks of human language. Yes it's occasionally annoying similar things have very disparate meanings, but English in particular is never going to shake them off.