Ok, I'm pretty sure that this has been happening to me for a while now, but since I don't do start topics very often, I didn't exactly realize there was a problem.
Starting a topic causes my browser to have some kind of error where the parent forum doesn't reload afterwords.  There have been occasions where I refreshed a minute or two later and somehow this caused a double post of the topic.  At least one of these was when I used the admin power to move a topic and ended up with two move announcement topics being generated.  
One of the places I browse from generates the following error (with some additional info that I don't think applies)
Network Error    
tcp_error   
 
 
Exception:   A communication error occurred: ""
  
Cause:    The Web Server may be down, too busy, or experiencing other problems preventing it from responding to requests. You may wish to try again at a later time.   
HTTP Error Code:   503   
Primary Contact:     Click here for additional guidance and procedures for requesting access to blocked content.   
  I did some tests in the curator section to see if this repeats, and to capture the above message since I had closed the tab it had happened to me on earlier.  One of the tests showed that when I generate a topic from my iPhone, I don't get the above message, I just get a blank page.