Person or Group field logic check

In response to this Workflow - send email on single field change?

You said to "create an additional field for project lead that is hidden from the forms. On item creation, a workflow populates this field with the value of the project lead.

Then you create an on change workflow that compares the project lead field with the hidden field. If they are the same, then you know a different field was updated and you simply end the workflow. If they are different, then you know this field was updated. You then email the user and then update the hidden field to the new value.

If the project lead is edited again, the workflow will refire and email the user."

I created this, but it isn't functioning properly. Is there something special SharePoint requires for "Person or Group" columns?