slilley on "twenty ten: spacing posts in archive view"

Using Twenty Ten with a Child Theme.

My posts are standard, but have a featured image -- which shows up as a thumbnail when someone tries to view a category page. The problem with the archive [category] view is that the posts with featured images do not have enough space below them. See here:

http://www.atmosphile.com/category/color/

Notice how the most recent one has a standard space below it, but the thumbnails seem to throw off the spacing on the other posts -- UNLESS the text of the post is long enough to run on below the thumbnail. Any thoughts, smart people? (Be gentle -- I'm a newbie.)