Git commit ef823fcb93d3f90cdb4e04441ecd5eff4be2f6a8.
The problem was caused because a CTRL+C launches the JVM shutdown process. JLine then attempts to register its own shutdown hook, which is illegal if the shutdown process has commenced.
I have fixed this by registering my own shutdown hook that maintains a boolean flag to indicate whether a shutdown has commenced. If a shutdown has commenced, the thread which fires JLineShell.doAnsiFlash(..) will terminate. Similarly if the thread had already invoked doAnsiFlash(..), there is a further check of the boolean flag just before the call to ConsoleReader. Together these seem to have resolved the problem.