The other mistake I was making was that the design tool that I am
working with seems to have a limit on its vertical height that it will
render.
Ther's another limit on vertical height which only occurs on Windows,
and which is imposed by the OS, not SWT. If your scrolled control goes
beyond 32767 (2^15-1) width or height then when you scroll beyond those
edges you will only see the default gray background. Just something to
watch out for.