thumbnail height not displaying correctly

Hi,
I am making a website with mainly images, using Twentyeleven. The site should be incredibly simple which means that I am only using the gallery function of WP itself, i.e. thumbnail are created from uploaded images,the thumbnails are linked to attachment pages.
I need to have the thumbnails defined with a maximum height rather than maximum width. The problem is, even though I have deleted all images (through ftp AND in the library), changed the preferences in Media to define them by height and “re”-uploaded them the gallery’s thumbnails are still displayed by the width which on the page becomes (I guess) 180px. The source-code displays them as having 180px in height!!! but the actual thumbnails are still 180px in width…
Why is this happening?
(I am not certain which version of WP I am using, can’t find it in the admin-panel..but think it must 3.3.2)

Having double-checked the size of the pictures by grabbing them from the thumbnail-page and opening in PS, the images are in fact 180px in height. But, they are still displayed as 180px wide on the page?!