beefy Beefy is broken?

I get the following error when running beefy in the simplest possible form, I'm on OSX El Capitan and Node 4.2.1.

beefy (v2.1.5) is listening on http://127.0.0.1:9966
200    7ms       530B  / (generated)
buffer.js:229
    buf.copy(buffer, pos);
        ^

TypeError: buf.copy is not a function
    at Function.Buffer.concat (buffer.js:229:9)
    at Stream.end (C:\Users\Tomasz\AppData\Roaming\npm\node_modules\beefy\lib\accumulate-error.js:25:26)
    at _end (C:\Users\Tomasz\AppData\Roaming\npm\node_modules\beefy\node_modules\through\index.js:61:9)
    at Stream.stream.end (C:\Users\Tomasz\AppData\Roaming\npm\node_modules\beefy\node_modules\through\index.js:70:5)
    at Stream.onend (stream.js:59:10)
    at emitNone (events.js:72:20)
    at Stream.emit (events.js:166:7)
    at drain (C:\Users\Tomasz\AppData\Roaming\npm\node_modules\beefy\node_modules\through\index.js:33:23)
    at Stream.stream.queue.stream.push (C:\Users\Tomasz\AppData\Roaming\npm\node_modules\beefy\node_modules\through\index.js:41:5)
    at Stream.end (C:\Users\Tomasz\AppData\Roaming\npm\node_modules\beefy\node_modules\through\index.js:17:35)
npm ERR! Test failed.  See above for more details.

The command I'm running is

beefy app/entry.js

Then when I request http://localhost:9966/bundle.js beefy crashes with the buf error above.

It's certainly possible I'm hitting some weird edge case, but it really seems like beefy is just broken on the most common development environments for versions of node released in the past ~3 months. Seems like a pretty big issue...