Hello Intcon ... i have visited your site , and i am having the exact same problem , you could note that if you clicked the title of the post and refresh it , it will refresh without the archive header.
My problem is that i have an ad laced on that page , and doesn't appear when the archive header version of the post is visible, only when i refresh the post by clicking the title does the ad show up.
My dilemma is that , how will a visiter know enough to refresh the post by clicking the title , therefore rendering my ad useless and invisible to the viewer.
Try it out , my site is http://windowtintingtoday.com
1) go to the site, you will see the home page with an adsense code obve the first post title.
2) go to categories and select a post to view , it will appear as an archive post.
3) Now... if you click the title of the post that appears , it will refresh and the adsense ad will now be visible.
The exact same thing happens with your site , exceptthat you have no ads on the original post.
But as i am writing this a light just came on , and maybe , this is something to do with the fact that we are selecting the post from the categories widget , and maybe we both have to activate the recent posts widget , in which the visitors to the site are more apt to select from , and that will show the original posts and not the archived posts , i think , lets try.