When you right-click an open window name in the Designer’s Project Browser, you get the following very clear options to Close & Commit or Close & Revert:
However, when you click on the Close button on the window tab at the bottom of the main Designer area, you get the following popup:
This dialog is a bit confusing - it is not immediately clear that pressing ‘No’ will in fact carry out a revert and you will lose any unsaved changes.
It might be an improvement if the dialog buttons were changed to ‘Commit’, ‘Revert’ and ‘Cancel’, maybe with a couple of lines of text explaining the difference between committing and reverting.