Unexpected MVC form submission behaviour

We are having an issue with all of our basic forms on the our site. They do not appear to be posting correctly - They appear to be posting to the homepage of the site with a querystring parameter '?sf_cntrl_id=xxxxxxxxxxxxxxxxxxxxxx'.

(An example of the form markup can be seen in the attached image snippet)

The only reference to this when trying to research the problem was found at this link:
survey.telerik.com/.../129931-sitefinity-mvc-beginformsitefinity-returns-a-query-string-parameter-sf-cntrl-id

Can anyone suggest why this may be happening? 

We are using Sitefinity 8.2

Thanks.