render boxes disappears until its finished [cycles]

Small annoyance I’ve come across.
So as we know when you hit render your tile size jumps around on screen and works on the image.
Like this:

Except in this one scene I get the orange box outline but I get no preview until the image is 100% done. Any ideas on why its doing this? I’ve tried appending to a new. In my other scenes it doesn’t do this.

Again this doesn’t exactly slow me down in any way but come animation time I’d like to see the images at a glance, you know?

Are you possibly set to a renderlayer or pass other than the combined pass on the current layer?

Thanks. Seems to have fixed it.

edit: its still doing it, crap.
edit: well now it seems append scene fixed it