When this issue occurs, the normal exit mechanism for QEMU (Ctrl+A+X) will not allow the user to exit QEMU. If this occurs, the process ID for QEMU must be identified and killed manually.
To identify the QEMU process ID, use a syntax such as:
$> ps ax | grep qemu
Once the proper process ID has been identified, it can be killed with:
$> kill process_id
After killing the QEMU process, the debugging/emulation session can be restarted.