(@ admin: Subject is no longer tied to resizing, so I created a new thread).
First have a good look at this portfolio image: http://www.thevelvetroom.dk/portfolio-item/kat-5/
Then open a new tab in your browser with this image inserted on a blog post: http://www.thevelvetroom.dk/kat-test-post/
Now you can A/B the two images, and I am sure you will find the difference obvious, even striking.
I you view the source code, you will see that both are showing the same image (http://www.thevelvetroom.dk/wp-content/uploads/2012/07/The_Duchess-3.jpg) which is NOT a thumbnail. Both are showing it at 609x406 which is the native size of the image.
So: The portfolio and the blog shows the same photo, but one does it rather badly while the other does the job perfectly. What is going on?
I hope you will give some priority to this question.
It has crossed my mind as a last resort to use blog posts for my portfolio, but I really hope you can sort this one out.