The header image is shown out of proportion in 1.5.5
See here the 1.5.5
you can see it here: http://www.udiburg.com/blog2
And here for the 1.5.2
You can see it here: http://blog.udiburg.com
These images are the same image. the settings of both are the same were the height of the image is set to 120px for both.
This happens also in landscape view.