Not really a bug or a feature, you just need to know how AC handles messages.
When you open the message from your nurse with the chart attached, a dialog box pops up, asking if you want to keep the message you are opening or delete it from your mailbox. That is your "moment of truth". If you think you might close the note by mistake, click "NO", and don't delete it. The message will stay in your box, and you are viewing a copy.
After you open the message, the program will only ask if you want to save the message/chart back to your mailbox if you have made changes -- even just clicking in a section of the opened chart is enough. Otherwise, if no changes, it will disappear if you close it, without a warning window.
However, even then -- all is not lost! You can find the deleted message/chart in the "Deleted Messages" part of your mailbox, until you log out of AC.
