I think i'm right in saying that Chrome creates a process for every extension or tab etc you have...
You may have to run a script at the end of your test to ensure its processes are killed using Terminate()
http://support.smartbear.com/viewarticle/30751/maybe something like:
if(Sys.WaitBrowser().Exists)
{
Aliases.browser.Terminate();
}
(asuming you're using name mapping/aliases).
Also you may find the following useful if you've not already seen them. They are articles about preparing the different web browsers before testing.
http://support.smartbear.com/viewarticle/26786/Hope this helps =)