This seems to be a bug with the lens blur filter, which has been seen in other threads here.
What if you were to precomp the depth layer and blur it a little?
Thanks for replying Andrew
Hmmm not good news. I tried the depth map blur method you suggest but it didnt seem to make any difference.
Yupp, you will have to try alternate ways or plug-ins, unfortunately.
Shame the developers cant find the time to fix stuff before releasing loads of new features