While writing unit-tests for MDL-45256, I discovered a bug in portfolio_rewrite_pluginfile_url_callback().

If a file is stored in a subfolder within the filearea, it's not found by this method. If its path is, say, /media/images/static/photo.png then the function throws "Couldn't find a file from the embedded path info ..." and it expects the file path is / and the filename is media/images/static/photo.png