Wrong Preview Size Landscape Pictures

Hello,
first of all thanks to that awesome Theme. I have come across an issue which you can see here
http://www.potatowurst.com/2013/02/21/beautiful-goa/goa-jan-kuhr-33/
the pictures (landscape) displays only in 900×75 instead of its full resolution 900×596. it does only happen with those pictures and not with portrait versions 596×900 px.
what could it be?
thanks in advance for help