I ran into this bug after trying several installations, and can confirm that it happens when compiz crashes during oem-config. As long as compiz is running (which you can tell by the window border and drop shadow), onboard works as expected. If compiz crashes during startup, however (which seems to happen randomly - sometimes it does, and sometimes it doesn't), onboard will only work with new windows that are opened (such as network preferences) when they gain focus. This is almost certainly a compiz issue.
I ran into this bug after trying several installations, and can confirm that it happens when compiz crashes during oem-config. As long as compiz is running (which you can tell by the window border and drop shadow), onboard works as expected. If compiz crashes during startup, however (which seems to happen randomly - sometimes it does, and sometimes it doesn't), onboard will only work with new windows that are opened (such as network preferences) when they gain focus. This is almost certainly a compiz issue.