In Open dialog, the button for Add does not have an accelerator key assigned.

The Add action allows for insertion of multiple files, in contrast to Enter key which actually accepts only one file. Steps to reproduce the Enter key problem:

1. Open the dialog, either via Media>Open, or the Add "+" button under the playlist.
2. Focus will be on location textbox. Press Down key once to focus the file list.
3. Navigate to where media files are, and use Shift+Up or Down to select multiple files.
4. Press Enter. Only the last selected file is added, not all the highlighted files.

Maybe this Enter behavior is a bug, but nevertheless, it's a good idea to add accelerator to the Add button if both Enter key and Add button are seperate actions.