It seems that the Box Blur filter in CS2 has a bug:

Open an image that has only backgound layer.
Duplicate the backgound as a layer.
Apply Box Blur with radius >= 181 on the new layer.

At r>=181:

- the previewbox in the filter dialog goes way (goes to transparent).

- the preview in the image window still seems to behave properly but after OK to the BB dialog the layer is totally transparent.

Jaska