I may have uncovered an undocumented behavioral change relating to Salesforce Content Libraries. Since we received the Spring '15 release, Salesforce is retaining the previous author when a new version of a document is uploaded by another user. Here's the scenario:

Prior to Spring '15:

1. User A uploads a document to a shared library.

2. User B uploads a new version of the same document.

3. User B is listed as the author of Version 2

4. User B is listed as the author in the library's "Recent Activity" and "Top Content" lists.

Since Spring '15:

1. User A uploads a document to a shared library.

2. User B uploads a new version of the same document.

3. User A is listed as the author of Version 2.

4. In the "Versions" tab, Version 2 is listed as "By User B on behalf of User A"

5. User A is listed as the author in the library's "Recent Activity" and "Top Content" lists.

In my org, no users have the privilege to upload documents on behalf of other users. True to that setting, the interface does not give my users the opportunity to change the author when uploading new documents or new versions of existing documents. It appears Salesforce is automatically retaining the last author of a document. That is different from the behavior experienced prior to Spring '15.

In another scenario where a document had two versions by different authors prior to the Spring '15 release, when Version 3 was uploaded after the Spring '15 release, it retained the author from Version 2.