Putting a version of an open source project into version control is not a fork, you could argue the same way that distributions are forking all software because they put them in packages. To fork you have to write code.
Putting it into public version control and accepting patches is a fork -- name it something new. If it's just a mirror, then call it that, and don't accept patches.
This is basic OSS politeness and the cultural norm. Only recently has Github trained people to think its OK to take someone else's work, keep the name, and siphon off interest/contributors.
If you want to fork, then do so. Treat it like the new project it is, instead of trading off the name and efforts of someone else, and operating independently of their development standards and norms.
Or, be polite, and accept that the choice of VCS is a stupid reason to fork someone else's project.
