>> I don't recall one ever being challenged as illegal.
Just because it has not been challenged would not mean it was not a violation. Eg. Prior to challenges, back-dating of option grants had been done for long enough that many people thought it was lawful. We now know it was not and you could get prosecuted unless you were Steven Jobs.
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There are times when rules and precedents cannot be broken; others when they cannot be adhered to with safety. (Thomas Joplin)