Switching to Visual Editor Deletes Post Content

When I create a new post, the usual default is the text editor. Whenever I click the visual editor tab, it switches, but the visual tool bar is missing and all the content text I entered is also missing. I can't place the curser in the content field at all.

If I switch back to the text editor, the content text is still gone, and now I can't click in the content field in this tab either.

I tried changing to the 2012 theme and disabling all plugins. Didn't solve the issue.

This has only begun happening sometime after June 23. I have the latest version of WordPress.

I need it fixed because most of the authors on the site canNOT use the text version as they know no HTML.