I encountered a puzzling-to-me situation: a gridpanel didn't have a vertical scroll-bar.

Poking around a little bit, I find that this happens when the grid doesn't know what its height is supposed to be.

The best overall solution was to add this to the configuration...
 anchor: '100% 100%'
This is, of course, a directive used by the "anchor" layout. (The oft-used "form" layout, by the way, is descended from that.) You do have to be sure that there is some layout specified, and if you're using a different layout you might need to do something different here.

So if those scroll bars ain't comin' to your network-neighborhood, think: size.