vf_open is called because Inline::Files redefines CORE::GLOBAL::open.

Perhaps your best option is to not use Inline::Files. Ever since I saw Brian Ingerson and Damian Conway present this at YAPC in Montreal, I've been of the opinion that the module is a nice trick, but not something I'd ever use in any serious program. Many of Damians modules don't work nice with other code - and this is another example. (But that's generally the case if you use source filters, add stuff in UNIVERSAL:: or overwrite core functions - you're bound to do something you didn't anticipate someone else does).