It has ever been thus. The Notes field is limited to 256 characters or a return character whence you will then see the ellipsis … indicating there is more text. Double clicking on this task will open Task Information and then Notes field for your additional information. I can’t see Microsoft ever changing this as the Tables which hold the Notes would become extremely unwieldy.
However, why don’t you list all the legitimate tasks in the normal way, indent them and then close them down so that only the Summary Task is shown?