HMR no workie for async reducer (counter)

[matgessel]

Repro:

1. start with vanilla clone of project
2. change /project.config.publicPath to 'http://localhost:3000/' (may be a firewall issue or just a Mac thing)
3. npm run start
4. browse to http://localhost:3000/counter
5. in src/routes/Counter/modules/counter.js, change COUNTER_INCREMENT (e.g. state + action.payload + 1)
6. click "Increment" button
   Expected: HMR reloads; Counter increments by 2
   Actual: HMR appears to reload, but Counter continues with original logic, incrementing by 1.
   [HMR] bundle rebuilding
   client.js?207a:207 [HMR] bundle rebuilt in 426ms
   process-update.js:27 [HMR] Checking for updates on the server...
   process-update.js:100 [HMR] Updated modules:
   process-update.js:102 [HMR] - ./src/routes/Counter/modules/counter.js
   process-update.js:102 [HMR] - ./src/routes/Counter/containers/CounterContainer.js
   process-update.js:102 [HMR] - ./src/routes/Counter/index.js
   process-update.js:102 [HMR] - ./src/routes/index.js
   process-update.js:107 [HMR] App is up to date.

• HMR does work for UI, e.g. changing button label in Counter.js.
• this issue was not caused by the Webpack 2 update; this test case also fails for the April 9 commit 1a4a71b.