use title content as existing field
The reason you can't use the title as you wish, is because it's not a Field, but a Property.

Unfortunately I can't find a meaningful explanation of the difference between the two at this time, so no link, sorry.

If it helps in any way, you can create your own title field, which will then behave more like you expect. Of course, you'll then have two "titles", so this will various annoying side effects.