Revision Comparision View show doc link field changed incorrectly

Problem: When comparing versions through 'Show revision history', even if there's no change in a link picker field selection, the comparing view shows the link picker has been changed, which is incorrect. The linked document is the same.

Reproduction Path:
1. Generate a project with archetype instructed in http://www.onehippo.org/trails/getting-started/hippo-essentials-getting-started.html with default values.
2. Go to CMS and create a new document type, testdocument, containing only two fields: one String field and the other Link compound field like the following:

3. Create a reference document (testdocument), "refdoc", which has set the String field to "reference document" and publish it like the following:

4. Create a new test document (testdocument), "test", which has set the String field to "test", and the link field to "refdoc" document like the following:


5. And publish the test document:

6. Edit the test document to change the title to "test 123" and save/close it like the following:

7. Open 'Show revision history'.

8. Select the previous version. And now you see the link field looks changed even if it was not changed. The UI also shows that the two linked doc names are the same: