Can you please specify in more detail the concrete information related to the blog posts that are causing trouble. It is not very clear form the explanation below whether you are talking about a BlogPost or an Event, since I see you mentioning EventStart several times, but there is no property EventStart for BlogPosts, can you clarify.
Generally a BlogPost will have a DateCreated (the one you see when you go to Content->Blogs->YourBlog->YourBlogPost in the Grid showing all posts in a blog) and PublicationDate. The archive widget is taking the PublicationDate for its sorting, please specify if you demand different fuctionality. There might be a problem with the PublicationDate of one of the states of a blog post differing from the others, that's why the problem with archive widget and information displayed on your page. Can you please verify if this problem occurs only for this particular blog post, or has multiple occurrences. If you could tell me some more details about the problem (specific steps to reproduce it and/or when was the post created, was it edited, etc. ) this will definitely help me give you a more specific answer, so please do not hesitate to write back.
the Telerik team