rounded corners on rectangular marquee and black border.

My rectangular marquee tool has started rounding the corners, and I can't fix it. Feather Selection is set to the minimum of 0.2 pixels. Smooth Selection is set to the minimum of  pixel. Interestingly, increasing those values has no effect on the rounding of the corners. The roundness remains unchanged no matter what I do.

While taking ascreen shot to include here, I found that it isleaving a large black border. I changed the Border Selection setting from 4 to 1, but the border persists.

What on Earth have I done, and how can I fix these problems?

Thanks for helping!