image field breaking auto url insert

Hi,
I have set up a parent child relationship hotel -> review.

All is good with link to child via display suite and review is prepopulated... great.

I then added a plain image field to the child and now the child is not prepopulated on save!

I can then add the parent by auto complete and the relationship is maintained.

Also the image isn't compulsory so if I create the child and don't fill the image field.. it works fine.

Just when I thought I was getting OK...bam, dam u drupal :)

Thanks for any help