After having reviewed a translated string, clicking the button "Submit" should updates the status of this string as "translated", and the counter for "translated" should be increased by one. In addition, the translated string should not be shown grayed out after a gray bar.
When you start your next translation session, those grayed out of your translated strings are prompted again, even though you have "Submitted" them.
Solution: uncheck the "Fuzzy" option when you are ready to submit.
One screenshot of this checkbox:
pootle-fuzzy.png