This has happened in two ways:
- 1 - any attempt to "Stop" any operation with the "Stop Hand" and "Yes"
2 - after selecting a second title to rip after the first completed successfully, it hung after ~30% in (progress bars). Clicking the "Stop Hand" and "Yes"
It did nothing - progress time kept marching on, bars remained fixed, no menu bar operation available. Quit gave another message to cancel, ansering "Yes" did exit but the optical drive also hung in Finder and can not eject the disc. Any further execution resumes immediately at the same exact point.
No way out but to reboot the system.