What the IFW report doesn't say is that there was a design fault on the securing clips/spigots fitted to the particular FEA-B wagons involved in this incident. It appears that the wagon manufacturer had misunderstood the UIC requirements and that the design had managed to get through all the approval procedures in force at the time.
The full report (heavy going
) is available here:
http://www.raib.gov.uk/cms_resources/0905021_R122009_Containers.pdf