I've definitely experienced issues on 7.0 with grids and summary block thumbnails not sizing properly, usually because of the amount of items or spacing issues. Sometimes it's within the default CSS that conflicts with other areas of the page. The scripts for these blocks are weird sometimes, even if you don't have conflicting Custom CSS.
This might help your problem:
#collection-597767a8a5790a133c13e5de {
#grid {
margin-top: 55px !important;
}
}
Hope this helps!
-Dan
