This is utterly bizarre behavior and I haven't found anything like it anywhere online. I've installed Cake DC with the Register page active. When I click anywhere on the register page, it immediately gives me a "You are not authorized" Flash message and redirects to the login form.
To be completely clear, this is NOT when I submit the form, it's when I click ANYWHERE on the Register form page. Same thing happens with Forgot Password page. I think it must be something simple but am completely stumped. I don't even know what code I should post.
Please check the source code of the page, it looks like something within your application layout is interfering with the form and submitting it.
Also check the console and try to disable javascript on the page to discard it's an issue with any existing js file loaded.
You can also override the registration form and set the layout to null, to ensure no code from your application is affecting that form.