1. Create a view and add for example
<a href="[[Site Web]]">[[Site Web]]</a>
where [[Site Web]] is a URL field. Save.
2. Test the view, click on the link, it will work fine.
3. Edit again the view. Add other stuff. Note that the above link has been transformed into:
<a href="%5B%5BSite%20Web%5D%5D">[[Site Web]]</a>
Save.
4. Test again the view. Click on the link: it doesn't work any more. The URL showed on the browser has become mod/dataform/%5B%5BSite%20Web%5D%5D
5. Edit and correct the view as above and it will work again.

I tested it on Moodle 2.8.3.