Using feeds and xpath to import multiple images into a node
The issue was resolved. 

Feeds importer was working correctly all along. The problem it seems was with the actual images themselves. I didn't realise, but the in some cases the source images where huge (in excess of 18Mb) It just co-incidentally happened that the large image was the second image for the node. Thus when the feeds importer failed. It actually looked like it worked but only managed to import the first image.

When I resized all the images and then re-imported them, it imported all the images correctly.

There is still an unresolved issue in that the import was failing silently. After a few tweaks import suddenly failed with server 500 errors. That's when the apache logs showed a memory allocation error. 

Once I saw that, I was able to determine the issue was related to the source images.

I guess the outcome of this is don't assume the problem is related to something you did.