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").