Problem Description: What is the problem?
What did you expect to happen: Why do you think this is a bug?
What happened instead: How is what happened different from what you expected?
Why is this bad/What are the consequences: Why do you think this is an important issue?
Steps to reproduce the problem: The most important section. Review everything you did leading up to causing the issue.
Possibly related stuff (which gamemode was it? What were you doing at the time? Was anything else out of the ordinary happening?): Anything else you can tell us.