It turns out rollup doesn't use the same algorithm for bundling commonjs files when there are cycles as node, which breaks postcss: https://twitter.com/Rich_Harris/status/869021144191561729. Webpack works just fine with it.
This sucks to have this rollup/webpack frankenstein but I really want to be able to release and don't really want to spend yet another day or two trying to make it work well.
Christopher Chedeau