When I select ignore on a files under version control it marks the parent directory as changes, then when I then do a commit, it checks in svn:ignore property to the repository, resulting in another revision.
Why do I need to commit the svn:ignore property? Is this a TortoiseSVN issue or just the way SVN works?
That's the way SVN works. When you commit an ignore, it automatically ignores that same file for others as well.
That's the way SVN works.
More information here:
http://svnbook.red-bean.com/en/1.5/svn.advanced.props.html#svn.advanced.props.workflow
Quote from that page:
As with file contents, your property changes are local modifications, made permanent only when you commit them to the repository with svn commit.
The idea is that, if you ignore a file, others will want to ignore the same file. Basically, what this means is that, system-wide, individuals will be ignoring the same files resulting in a more consistent development environment (and a cleaner repository as developers won't check in personal files, etc that are generated by IDEs, their testing files, etc).