Thank you for creating this plugin!
I tried to use your register-form.php template to create a custom register page under a sub-site in a multisite network. I copied register-form.php into current theme's folder, then I created a page called Login (http://main-site.com/sub-site/login), and added this line of shortcode:
[theme-my-login register_template="my-register-form.php"]
The login page shows customized template fine, but when I click on Register link (http://main-site.com/sub-site/login?action=register) in that page, it gets redirected to main-site's register page (http://main-site.com/login?action=register). My expected action is to stay in sub-site, and show register-form.php template. How do I solve the problem?