I've been debugging an issue where transforms wouldn't get applied in Windows, and I've tracked it down to this regexp:

var row = typeof file === 'object'
    ? xtend(file, opts)
    : (/^[\/.]/.test(file)
        ? xtend(opts, { file: file })
        : xtend(opts, { id: file })
    );

For example, /Users/me/index.js passes this test but C:\Users\me\index.js fails.

In my case, row.file ended up being undefined which caused transforms to be skipped silently.