Photoshop crop has blurred/feathered edge

I have occasionally been having a problem in Photoshop where the edges of a cropped image are feathered by a couple of pixels. Not a big deal on images that are thousands of pixels on a side but it's a big problem when making 150x150px head shots for online profiles. This appears to happen when the crop starts at the edge of the image and the layer is unlocked (eg: not the Background layer). You can see the feathered edges at the bottom and right edges of this crop. Feather for the marquee tool is 0px and anti-alias is off if that matters since the Crop tool has no feather or anti-alias options.

This is Photoshop CS 5.5, but I recall having this problem on and off ever since we got transparent layers in Photoshop 4.