I'm not too great with this sort of stuff but if one coil is still misfiring does that not point to one still being faulty? Where they all brand new parts you fitted? Failing that ita the coilpack I would of thought it would be somewhere further up the line before the coil causing that one coil to niwt function properly.
Try giving it a Google if you havnt already, the NZ sideman have some more answers. Most problems I've come across with my altezza multiple people have had the same problem on there and may be able to help you out more than I can