My ribs are playing up again, so perhaps it's better if I post this https://feedback.photoshop.com/photoshop_family/topics/adding_sub_keywords_in_bridge_4_also_adds_parent which explains my problem. I have automatic parent keywords turned off in Bridge. When LR detects I've added sub keywords, it produces the warning message (I have a smart collection for that) and I tell it to import metadata from file. The problem is that when I look back in Bridge, the parent keywords have been checked. I delete the unwanted parent keywords in Bridge, LR detects a change and... I think I've finally figured it out. I now have save metadata to file on automatic. Before this I could eventually get the problem sorted. Now I think LR detects metadata changes, I opt to import from file, that metadata is written to the LR catalogue and then that change is automatically written back. I found out on the LR Queen forums that LR can sometimes flatten hierachical keywords, which is what I assume it's doing by checking the parent keywords back in Bridge. I've turned automatic save off...
