Photoshop :: Removing Lens Blur Halos In Shallow Photo

I'm working on a portait where I want to give it a more shallow DOF (depth of field) than originally shot. In other words: I want to turn the background blurry while the foreground and subject should be sharp. I decided to use the Lens blur filter (Filter-Blur-Lens blur) for this.
 
Basically I just duplicated the image to a new layer, turned that layer into a smart object, added lens blur to it, then used a gradient filter on the mask in order to make the blur fade away in the front (just like a camera lens wide open would). Finally I used a brush to carefully remove (mask) the blur from the subject, revealing the (unblurred original image) bottom layer.
 
The problem is that the blurred layer also introduces a "halo" around things which isn't very attractive (see screenshots below). Is there a way to make the background blurry without adding halos? I've tried Gaussian blur as well but the same problem was there. I'm using Photoshop CS4 on a Mac.
 
Original image

Duplicated layer blurred (lens blur) -notice dark "halo" above hair
 
Masked to reveal sharp (original) layer for subject. The halo is of course still there. Not very flattering