Earlier today I ran into a problem with the application I'm working on and found the same behavior in the demo page for the splitter.
In a splitter with 2 panes, move the splitterbar between the two panes. Add a third pane to the right hand side and move the splitterbar between the second and third pane. Close the third pane and move the splitterbar between the first two panes again.
If you add a pane to the right hand side again, it will have a width of 0. The demopage will show a splitterbar on the right side, outside of the splitter-div, which allows you to adjust the width and make the thrid pane visible.
In my application, the splitter fills up the screen to the edge on the right side, so in my case, the splitbar will be invisible as well.
How can I fix this?