This was by design, for the reason that argv0 pointed out - if you type in $false, $cancel, and so on, in an editbox, that is in fact data and there's no way to tell the difference. I can't change that behaviour since it might break existing scripts, which is something I try to avoid. I can however add a new switch which behaves the way you are asking. I will add that to my to-do list for the next version.
