Problems with edge clarity of photos

[Geoff Port]

Hey all,
I've been noticing that some of my photos are not as sharp at the edges as others. I have included a shot of our town library I took yesterday morning. While tickling it up I noted that the left background of the building was not sharply focused and I couldn't tweek to make it any better.
I would have thought that at f16 everything from front to back left to right should be sharp. There is also a degree of offset/ out of register, in that area.ie; a partial ghost of posts.
The shot was taken on tripod and with an IR remote with AF and Stabilization both engaged.
This only seems to appear with photos that are busy across the entire shot. Landscapes with out large amounts of subject matter at the edges don't seem to be effected but maybe thats just because theres nothing in shot to show it up.
Q1: Is this problem my because of something I am doing wrong?
Q2: Could it be the lens (Canon 18-55mm f3.5-5.6 IS II) a kit lens that came with the camera and remarkable cheap.


File Size: 292 kb - 1023 x 682
Camera Make: Canon
Camera Model: Canon EOS 60D
Date/Time: 2012:08:25 08:38:30
Resolution: 1023 x 682
Flash Used: No
Focal Length: 18.0mm (35mm equivalent: 28mm...
CCD Width: 22.99mm
Exposure Time: 0.017 s (1/60)
Aperture: f/16.0
ISO Equiv.: 100
Whitebalance: Manual
Metering Mode: center weight
Exposure: Manual
Exposure Mode: Manual