Joe,
Thanks for the reply - nice to know it's not me!
I tried a few more variations since posting the query, but with the same results. I've set the extraction modes to only pick blocks with attributes, from model space, etc. and for these trials the blocks are only on Layer 0.
I have also tried the same blocks on AutoCAD Architecture 2009 - the attribute extraction works fine including populating all the cells in the inserted table. Looks as though it's a bug in 2008.