Reproduce bug:

npm install
# or
yarn install

# Make sure Flow isn't running (the bug only happens if a Flow server isn't running)
npm run stop

# Try calling Flow from Node
node run-flow.js

Flow (called with Node's spawnSync) never exits, so the command hangs.

The problem started in Flow 0.71, so the command will succeed with Flow 0.70.

Note: This is a Windows-only bug.