As far as I can tell, this is string-searching for "global" and switching behaviour as a result.

My builds started failing because I had a JS comment that contained the word "global".

The error suggested the failure was when it tried to parse an async function - not sure why it failed there, but if I delete "global" from a previous comment everything works again.

Here's my rollup config:

return rollup({
  entry: src,
  sourceMap: true,
  cache,
  format: 'iife',
  plugins: [
    nodeResolve({
      preferBuiltins: false,
      browser: true,
      jsnext: true,
      main: true
    }),
    commonjs(),
    rollupBabel({
      presets: ['stage-3', ['es2015', {modules: false}]],
      plugins: [["transform-react-jsx", {pragma:"h"}], "external-helpers"]
    })
  ]
})

I've added {ignoreGlobal: true} to commonjs to fix things in the meantime.