Earlier: "... random ... press the save button [after editing] it says 'This is only a preview; changes have not yet been saved! ', but the rest of the content is disappeared..."
Peter Blaise responds: Corrupt browser - Microsoft Internet Explorer. Try another system, try rebuilding, and cleansing all temp and cache files in your current browser editor system. Windows? Reboot in safe mode and clean there. Worked for us. Also, Mozilla Firefox worked for me flawlessly all the time, so I stopped troubleshooting MSIE (pronounced "MiSerIE").
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