Strake - that did occur to me as I still have the green stub but the last three times I have travelled to the States it has not been taken off me. This may be a red herring as my wife successfully applied and she still has her green stub in her passport!
Various other forums suggest it is the passport update thing and waiting 10 days to re-apply to avoid highlighting yourself making multiple entries.
I am loathed to call the US Embassy for the same reason, maybe I will try BA.