Cover Image missing & videos showing on blog list page?

Hi SI Team

Please go here:

http://finalbug.net/blog

And note that some of the posts no longer show the Cover Image.
Instead they show any videos in the Blog Post!

http://finalbug.net/blog/entry/479-roles-beyond-with-role-o-matic
http://finalbug.net/blog/entry/475-nle-tracks-roles-part-3-of-3
http://finalbug.net/blog/entry/472-nle-tracks-roles-part-2-of-3
http://finalbug.net/blog/entry/471-nle-tracks-roles-part-1-of-3

Exceptions being as follows:

http://finalbug.net/blog/entry/401-edit-in-resolve-the-fcp-way-part-02
http://finalbug.net/blog/entry/400-edit-in-resolve-the-fcp-way-part-01

I suspect that this is basically happening to posts that were created in EB 5.0.X

I just updated from 5.0.25 to Version: 5.0.26 so maybe this is related.

Please advise

thanks in advance

Paul