If you are unsure whether the behavior is really incorrect, you can ask on dev@platform.netbeans.org. Do not be too shy to file a bug, though; it is just as easy to close an invalid bug report as it is to reply to the mailing list.

If at all possible, figure out how to reproduce your bug. From scratch: the assignee of the bug report cannot see your computer and has no idea what you are working on or why. Try to make a minimal, self-contained test case that anyone could run to see the bug in action. Often a suite project is a good test case - attach a ZIP of sources, including nested module projects. If you know how to write a unit test for the buggy module, that is ideal, but this can require some deeper knowledge of NetBeans internals. Sometimes a bug occurs that just cannot be easily reproduced - it is still fine to file a bug, but include as much diagnostic information as you can and do not be surprised if it does not get fixed.

Read: Issue Reporting Guidelines

For general background you may also want to read: How To Ask Questions The Smart Way

File a bug report and include at least

Some background on what you are trying to accomplish and why.

Some kind of test case to demonstrate the bug.

Instructions for running the test case.

What you would expect to see happen.

What you actually see happen.

Be patient as the bug is assigned and evaluated, and provide additional information if requested. If all goes well it should be fixed for a future NetBeans release. The evaluator may also be able to offer some workarounds for use in current releases.