I discovered this one quite by mistake. I debated posting it as a bug report or as a feature request. It could I suppose be considered a bug. While editing a multipage webpage I accidentally clicked on the "new page" tab. Before I could do anyting allmy changes where gone. I am assuming if I had clicked on any of the other page tabs the same thing would happen.
Could a warning box be put so that if you click on a new tab in the web page menu with unsaved changes in the current page you will be asked to go back and save your changes. It may be that you have decided not to save your changes so the warning box should allow you to click through and leave the page unchanged.