When I update a post the permalink changes breaking the url. Why?

Hi there,

I am having a problem with my permalinks. The permalink structure that I have for my posts is – Month and name (common setting).

When I create a post the month and name setting works fine, inputting the correct values i.e. mysite.com/2014/03/sample-post/

Now when I try and make a correction and update the post the permalink changes to mysite.com/-0001/11/sample-post/ – meaning the post can no longer be found.

The site is an international/multilingual site using WPML. I also have bullet proof security installed, latest versions of each. htaccess is writeable but secure .htaccess is enabled.

Could anyone give me a clue as to what might be happening?

Thanks.