SIGINT is sent twice when pressing Ctrl-C, causing dirty shutdown

I have a package.json with the following scripts:

…
"startemulators": "firebase emulators:start --import seed",
"listen": "onchange 'source_files/*.js' -- touch functions/index.js",
"emulate": "concurrently \"npm run startemulators\" \"npm run listen\""
…

Running the emulate script works as expected, but pressing Ctrl-C to shut the processes down gives me this:

[0] i  emulators: Received SIGINT (Ctrl-C) for the first time. Starting a clean shutdown.
[0] i  emulators: Please wait for a clean shutdown or send the SIGINT (Ctrl-C) signal again to stop right now.
[0] i  emulators: Shutting down emulators.
[0] i  ui: Stopping Emulator UI
[0] ⚠  Emulator UI has exited upon receiving signal: SIGINT
[0] i  functions: Stopping Functions Emulator
[0] i  hosting: Stopping Hosting Emulator
[0] i  database: Stopping Database Emulator
[1] npm run listen exited with code 0
[0]  
[0] ⚠  emulators: Received SIGINT (Ctrl-C) 2 times. You have forced the Emulator Suite to exit without waiting for 3 subprocesses to finish.

So for some reason, a second SIGINT is sent to the firebase command specified in the first script. How come?

Reproduce the issue from package.json by running npm run emulate and pressing Ctrl-C once. Trace how concurrently forwards signals to the Firebase emulator and the onchange process, then verify shutdown completes without Firebase reporting a second SIGINT or forcing unfinished subprocesses to exit.