The metadata “mgnl:lastModifiedBy” is lost when publishing a page between author & public instance. If we edit a page (eg, travel/about) with superuser and then we publish it we have the following scenario:

• Author instance: mgnl:lastModifiedBy is superuser
• Public instance: mgnl:lastModifiedBy is anonymous

Workaround
Create a command to copy the data to a dedicated property. This command could be added to the publication command chain to run first. It would subsequently become part of the node's version and then activated when the workflow is approved (or when the node is published).