There are a lot of reasons one might vote to close a post. We've actually scaled back on list of close reasons because it became to daunting for the average user to choose from a long, detailed list.
Use the built-in tools
I would suggest closing bug reports as "Off Topic" (because that's what they are) and use the question-comments to provide the bug report URLs and to instruct the user as to the proper procedure for reporting bugs. That will quickly become part of the community routine (to close bug reports and add the comments) and soon everyone will be following suit.
Don't forget message editing/wiki
The community can adopt whatever conventions you choose to help guide bug-report posts. When a post is closed as an off-topic bug report, you can add whatever you feel would be helpful to the top of the post. For example:
This question was closed by fluteflute as actually Bug #1.
Bug reports are off-topic for this forum. The Ubuntu Wiki has a very thorough guide on how to report bugs.
Every time you do that, you are leaving a "sign post" for everyone to see, instructing them how to proceed in the future. Soon it will become the community convention and everyone will be pitching in to keep the site clean and helping new users along the way.
There are hundreds of little conventions that have been adopted this way. You don't notice them because they just seem second nature once everyone starts following along.