canon 10-22 corner sharpness

Hi, I just bought a second hand canon 10-22 F3.5-4.5, while I am very please with the color and sharpness(center), I have discovery some blur corner on some of the images especially when I focus on far object. Here are two sample, is this normal ?

This is shot at F4.5, notice the riight side of the image, there are some weird out of focus issue. The top of the image is also blur.

This one is shot at F5, while the center is excellent, its blur on the right of the image.

Sorry for the large files...

Regards,
KS