Example: When adding a Jar or Folder to Project Classpath (project -> Properties -> Java Sources Classpath,) when you Move Up or Move Down, the selected items can go off screen. You must stop and manually scroll to find them.
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