firefox.real starts using a lot of CPU after "Tor unexpectedly exited"

I am using Tor Browser 12.0a2 for linux.

1. Start the browser and let it bootstrap.
2. Find the PID of the browser's tor process and kill it from the command line.
3. Tor Browser shows a "Tor unexpectedly exited" dialog, and then the firefox.real process starts using >100% CPU. The high CPU use continues even after clicking the "Restart" button to restart tor.