You don't need that box, just select a note by clicking on it and use the mouse wheel to adjust the sustain (or you can use the keyboard key [ or ] too).
The note panel, as i said, is useless for adjusting sustain.
I don't know how else i can write this anymore really.
Woudln't work with a traking pad on my laptop. And I could not figure out which key is the [or]. Needed a USB mouse to get it work. Eureka!!! It works. Better yet I, it also works with "Select All" so can change every note at once.