Optimistic Locking is not working when using Repository save method

Optimistic Locking doesn't appear to be working any longer when using the repository "save" method to save an entity. This was previously working in the 1.4 release.

Steps to reproduce:
-Create a Document class with the @Version annotation
-Create a CrudRepository referencing the Document class
-Load an existing document via the repository "findOne" method in thread 1 (validated the cas is set in this document)
-In thread 2 update the same document
-In thread 1, save the document using the repository "save" method

Expected Result:
A CASMismatchException is thrown

Actual Result:
No exception is thrown and thread 1 overwrites the document thread 2 had saved

Note: this exact scenario was working in 1.4 release