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No worries. I had a poke around the import code and I think I 
found the problem: 

backends.rdbms_common.Database.import_list, where "is 
retired" is true, updates the __retired__ flag to 1 first and 
then does an addnode which promptly sets __retired__ back 
to 0.

Switching the order of the addnode and the retire leads to an 
import which (at least at cursory examination) is as expected 
and correctly keeps retired nodes retired.