Paste without formatting broken

While Myriad is the font which is selected in a fresh install, when you haven't yet changed to something else yet, Photoshop doesn't really have a default setting for the typeface. Like most tool options in Photoshop, the font is "sticky." This means it remembers whatever the last setting was. Change it to Arial? All new text boxes will be Arial until you change it to something else. Photoshop doesn't pull in information from other applications regarding font styling. It just applies the last used settings.

Really.... the default should be easier to manage through dropdown by adding Set Default Typeface...