There's a thread running on this very subject here:
Barry Hempel
to summarise, a CPL had a traumatic head injury causing epilepsy and refused to stop flying, while at the same time the regulatory authority (CASA) knew all the facts but failed to act and stop him flying. It makes for interesting reading.
Oh, and the reason why the thread was started?
Barry killed himself AND his paying passenger while on an "Adventure Flight", and it all came to light during the Coronial Inquest (in Brisbane Australia).