Clearly an issue with the bounding box and live corners.
I have no solution - I think only Adobe can address this since it appears to be a drawing issue with live shape bounds and the Bounding box. Expanding appears to be the only way to correct what the Bounding Box sees as the "bounds".
However, why do you even need the Bounding Box???
The Bounding box is worthless for everything other than resizing area text frames. The only unique thing the Bounding Box will do is resize an area text box without transforming the text within it. That's it. There's nothing else the Bounding Box does that can't be done in other, just as easy, ways.
Turn off the Bounding Box (View > Hide Bounding Box). This is the first thing I do when I launch Illustrator after installing it.
If you need handles to scale/rotate etc, tap the E key and use the Free Transform tool... same basic thing with additional benefits and it doesn't suffer from this bounding error.
The Bounding Box was only ever added to Illustrator (CS4 by the way) to make CorelDraw users feel more comfortable when they switched. It never existed prior to that and wasn't needed. And Adobe hasn't added any new features to it since it's introduction. The Bounding Box, as a whole, is an unnecessary feature.