If creating a ShellToast with a Title of more than 64 characters (including any whitespace) then the toast will be displayed but the title will not be shown.
If Content is specified this will still be displayed. If no Content is specified then the toast will just include the application icon.
This is both undocumented and unexpected behaviour.
It's particularly unexpected as deliberately specifying an empty string for the title causes an error.
I'm not sure if this is a bug or a built in back door to avoid displaying the title. Either way this worth being aware of when working with toasts.