My alpha vfs dir on my windows dev machine is currently about ~1.5G so if the issue is still around on beta, I think you should file a JIRA issue.
More details please. How are you starting the server? How are you restarting it? Have you done any config changes (for example to the JAVA_OPTS in the config files)?
In my case, I haven't done any significant changes. I start and stop the AS from Eclipse Kepler M7, lots of stuff left behind in the vfs folders. I have a 1M tree /f dump of it...
I added my DataSource and jms configs to the standalone-full.xml Those are the only changes I've really made to that.
As for starting it up. I'm using the standalone.sh to launch it for testing and then I just hit control-C, but I've also used the cli -connect command=:shutdown method.
I get the same result both ways.
The folders just keep stacking up in tmp/vfs