How can I debug why user_save() is being called twice?

Question

I have a site with a large number of modules (100+) installed and I have an issue with my rules firing twice, which appears to be caused by user_save() being called twice. (I was able to confirm this by adding a dpm($account) in user_save(), which is printed to the screen twice on my dev site when I log in as an authenticated user and update that user's profile.

Now I'd like to find which contrib module is caused user_save() to be called twice (of course this assumes it is a contrib module). I'm not a developer so I'm getting stuck. I have Netbeans set up with Xdebug and I set a breakpoint on user_save(). Then I started the debugger and logged in and updated a user account, but when I look at the call stack I see the following:

/mysite/modules/user/user.module.include_once:424 /mysite/includes/bootstrap.inc.drupal_load:1126
/mysite/sites/all/modules/contrib/devel/devel.module.devel_boot:616
/mysite/includes/module.inc.call_user_func_array:833
/mysite/includes/module.inc.module_invoke:833 /mysite/includes/bootstrap.inc.bootstrap_invoke_all:1097
/mysite/includes/bootstrap.inc._drupal_bootstrap_page_header:2454 /mysite/includes/bootstrap.inc.drupal_bootstrap:2214
/mysite/index.php.{main}:20

And then when user_save() is called again (in the same page load) I see exactly the same output. If it is a contrib module that is causing user_save() to be called twice, how can I find out which one it is?