Keyword Field always shows the value of the last version.
Steps to reproduce:
1. Create a Content Type with an `ezkeyword` Field
2. Create a Content item with Keyword "one" in the Field.
3. Publish the Content item.
4. Edit the Content item and add keyword "two" to the Field.
5. Publish the version.
6. In Versions tab, click "Restore Archived Version" on the archived version no 1
The Keyword Field shows only value "one" that was saved in version 1.
The Keyword Field shows both "one" and "two" keywords.