Nige 321 and Grumanniser - yes, having re-read it, that is what the report says so the question is why did the bearing fail?
Airsound, as I understand the system, you have two shafts, one inside the other - one just goes in and out (control rod for pitch change) which is the inner one and the other spins around it to transmit the drive from the TR driveshaft to spin the TR.
The duplex bearing allows the inner (control) shaft to move longitudinally in the outer (driving) shaft so that you can superimpose pitch change inputs onto the spinning TR.
If the bearing seizes, the driving shaft starts to turn the control shaft and that is what broke the split pin and allowed the castellated nut to undo.
Presumably the extra drag on the driving shaft is what caused the spider end nut to tighten too much.