In BlogListPosts.xslt the <abbr> tags used for the entry dates have incorrect syntax :
 
title="umbraco.library:ShortDate($post/PostDate"
Missing closing round bracket & the whole thing in quotes should be surrounded by curly brackets.
 
Also, the proper usage of the abbr tag is the other way around - the abbreviation (short date) would be inside the tag while the full date would be shown as the title.