When you open a new Java file in the editor, there is a green box in the top-right corner of the scrollbar which indicates the lack of compiler/hint warnings and errors. This box is yellow for warnings and red for errors.

The problem is that this box is initially green when the file is opened, even though compiler/hint annotations are out of date. Similarly, when the file is edited the annotations are out of date for a few seconds. In both these cases, Netbeans should use a different color (or UI element) to indicate ongoing processing so users don't mistakenly believe that the file contains no warnings/errors and move on to looking at the next file.