To exit the editor always use SAVE or CANCEL. Don't close the main window of the browser while editing (may create errors). If you are online for a long time use Apply (save without closing the editor).
Do the safety copy of your article. The icon HTML displays
the full code of the site. Using Copy (CTRL + C) and Insert (CTRL +
V) you can write down the code on your hard drive. When
things goes bad you can restore the code and recover the site.