Users should not become "Last Contributor" when tagging a document

Steps to reproduce in Web UI or JSF:

• As a user that has ReadOnly access on a document:
• Create a tag and add it to the document.
  => ReadOnly user is listed as the Last Contributor on the document.
  => Under the Activity thread, ReadOnly user is listed as having modified the document.

If tagging a document is categorized as contributing to or modifying a document, then by definition, a user with Read Only access shouldn't be able to tag a document. Otherwise, tagging should not change the contributors nor be listed as a modification in the audit.