That actually meant that your message has been received, not read. But as Facebook has took the responsibility under their hands, it seems that they actually understood what people thought and with the new update, those check-marks will work the way you previously they did!
According to the new update, the sent message will have:
Single check-mark if message is sent (check-mark color- black, light grey). Double check-mark if the message is received (check-mark color- black, light grey). Double check-mark will turn blue once the message has been opened.
The new developers are really interesting, working according to “actual user experience”.
