change the css version to 3.3.2 in this plunker code and the backdrop won't appear when you open the modal.

from

```
<link href="//netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css" rel="stylesheet">

```

to

```
<link href="//netdna.bootstrapcdn.com/bootstrap/3.3.2/css/bootstrap.min.css" rel="stylesheet">

```

<http://plnkr.co/edit/rzU6gQsjEP4R9sGKO2dl>