When you want to edit an app, a new browser window is opened for the development environment. After editing and then closing the app you are returned to the PowerApps home page in the same tab. This tab is usually redundant since the original tab will still be open with a model dialog prompting you to confirm you have finished editing the app. When closing the second tab, however, you are prompted that you are leaving the site and that changes you have made may not be saved. This seems to be redundant, since no changes have been made.