Often, when I create a new project as a tab in Photoshop, whatever my first project that was open will stay on the screen, but will not be interactive. Switching tabs doesn't change the appearance of the screen. The only way to change the appearance of the screen is to undock the tab and bring the first project into a window. Even after this, the original project never visually updates (though the project still is active—I can copy/paste, save, etc.). The only way to fix it is to close all projects and restart the program.