defocus node

I Been playing with the defocus node as of late. Every once in a while i run into this nasty issue. The transition of the input z-depth isn’t smoothly blurred. Another words, it’s like it gets to a certain distance then blatantly stops blurring without a smooth transition. Only seems to happen if I’m working with high blur values.

If it happens again I’ll post a screenshot.

this post should be redirected to this thread, where the same problem is addressed: http://blenderartists.org/forum/showthread.php?t=108584