Regression in recent dev builds, I think. JDK 7u4, Ubuntu, Ocean.
When in a *.java editor I press Ctrl-7, the Navigator window has no apparent focus; at least arrow keys do not work to scroll between members.
Workaround: Ctrl-0 Ctrl-7. (The window has proper focus thereafter.)
This old bug may not be relevant anymore. If you can still reproduce it in 8.2 development builds please reopen this issue.
Thanks for your cooperation,
NetBeans IDE 8.2 Release Boss