I installed today the last version of the WindowBuilder add-on on my Eclipse and I keep having this annoying problem where I can't see the whole JFrame in Desing mode. If I try to resize it, it doesn't solve it. It's like if I only had access to see a corner of the JFrame. I don't seem to have a problem with JPanels so far. Please check the picture to see the problem.
I tried reinstalling several times both Eclipse and WindowBuilder but it still doesn't work.
JPanel sometimes has issues working with other applications. Try uninstalling WindowBuilder and seeing if it works or switch to another IDE