Reading the TSB report about that time an A310's rudder flew the coop, I came across this piece of background information (section 220.127.116.11, History of Earlier Design Aramid Fibre-Reinforced Plastic Rudders):
In the earlier design of the rudder, GFRP [glass-fibre-reinforced plastic] was used as the bridging layer between honeycomb and CFRP [carbon-fibre-reinforced plastic] only in the reinforced region around the hydraulic actuators. Elsewhere, AFRP [aramid-fibre-reinforced plastic] was used. The AFRP system resulted in poor bond strength of the interior skin. Those rudders experienced large in-service disbonds of the inner skins. [...]
What made A300/A310 rudders using AFRP so prone to the rudder skin delaminating from the underlying structual framework?