gezap

Found out the solution by myself.

The images were shrinked with one pixel by the browser. So thumbnails with 322px becomes 321px and thus creating the blurriness.

Solutions:
When adjusting the theme for your purpose check which thumbnails/images that create problem. Check how wide they are when presented in the browser not as they are as file. Adjust the numbers accordingly in the functions.php.
Search for the add_image_size( 'teaser-thumb', 332, and change the number.

Another solution is also to adjust the width of the columns in css. Add this as far I have solved under Custom CSS in Theme Options

.threecol {
    width: 33.38%;
}

.gallery-columns-2 .gallery-item {
    width: 45.2%;
}