When using a non-translatable content object xmlblock attribute with urls, creating a new translation will result in stale/invalid site link.

Steps to reproduce

1. Setup a content class with a non-translatable xmlblock attribute
2. Create a content object, in language eng with a link in xmlblock using url http://testurl.v1.en
3. Create and publish new translation of the object in any other language (Version 2) - the xmlblock attribute cannot be modified.
4. Publish an additional version (3), in english once more, changing the url to http://testurl.v3.en