Angular JS: URL parameter appears before the `#!/` and doesn't appear in $location.search()

I'm integrating a small existing Angular JS app made by someone else into an exiting website that was not built with Angular.

All the Angular JS app files are kept in a completely separate directory and then the user can click on a link to take them to the index of that sub directory. For example:

<a href="/path/to/angular-app/?returnUrl=/original/location">Login.</a>

As you can see above, I need to pass a URL parameter called returnUrl. I then need to pick up this value in the Angular JS app, using:

$location.search()

However, this actually returns an empty object. I think it's because the Angular JS is appending #!/login on the URL after the URL parameter, like so:

example.com/path/to/app?returnUrl=/original/location/#!/login

If I modify the URL in the browser, moving the returnUrl parameter to the end of the URL and refresh the page, it works and $location.search() returns {returnUrl: "/original/location/"}. However, as far as I can see I'm not able to change this in my website because the parameter is part of the link to the Angular JS app and #!/login is added afterwards automatically.

I'm new AngularJS, so please explain as clearly as you can:

1. What is going on here? And why is the URL parameter before the #!/login?
2. Why does this prevent $location.search() from returning anything? If I move the param to the end of the resulting URL, it works.
3. What can I do to fix this?