The facts:
Okay, you’ve deactived all plugins and changed themes and it still has
the same issue.
You know the posts have content cause there is content inside of the [HTML] tab “What I have discovered is that if I block select a section the html version of the content appears,”
You’ve tried this on two different machines. (your laptop you said)
—
The debug:
I have seen this happen when there is content inside of the post that is pasted from say “Word”.
I have seen this happen when inappropriate js files are loaded (but loaded by plugin or theme) but you disabled those.
More information:
command-A (i think)(for mac) and control-R (for PC) reload “reget” all of the scripts and css files to the local browser you are using.
Switch themes back to twentyeleven and refresh the editor page using the command for your browser to reget those .js / css files of the post editor. It’s possible they are cache’d on your side and you are maybe using a corrupted one.
Check the contents of the posts, check if there is any non-standard html in them. You said you can do this by “highlighting” the section and you can see them. That is what you gave us in defining that content actually exists.
I assume your site has the ‘outputted’ content displaying on the site, if there’s a chance for a link to your site to see that content on the ‘end user’ visitor side that would be great.