It's a balmy 7 degrees Fahrenheit in Chicagoland as I write this, so it's sort of appropriate to write about how lead status in Pardot "freezes" when it's converted to a contact.
The setup to this scenario is you've created a custom field in Pardot to map to the standard Lead Status (API name "Status") field in Salesforce. As long as the record remains a lead, there's no issues.
However, you may have noticed something strange to leads that are converted to contacts. Let's say for the sake of this example that the "converted status" of a lead is named "SQL".
Here's the Salesforce Lead Status field setup with custom values. When a lead is converted, Salesforce places it in the status "SQL" because that's the "Converted" status.
Here's where it gets chilly: once a lead is converted to a contact, it ceases to be a lead anymore and all Pardot's subsequent sync activity is with the contact. And guess what? There's no lead status field on contact.
So Pardot has no further information on that converted lead status, and as a result, your custom field remains forever frozen at whatever it was before it was converted (say, working from the example above). So it will never change to SQL.
Now, if you were to run a converted lead report, you'd see that all your converted leads actually do have a status of "SQL". It's just Pardot that has no idea the change was made, because it's talking to the contact now, and contact has no information on what the lead status was.
How to fix this? You might think-- well, just create a custom field on contact and map it there. The problem is you can't create custom mappings for standard fields! Fortunately there's a pretty simple fix using an automation rule in Pardot.
The rule simply looks for when a Pardot record becomes a contact, and where the lead status isn't the converted status, and changes it to our "converted" value of SQL.
The reason we have the "Lead Status is not Empty" rule in there is we don't necessarily want to have a value in lead status the prospect was always a contact and never a lead. So if it's a contact with no value there, it will leave it alone. You only need to run this automation rule once, no repeating necessary.
Hopefully this helps you thaw out all those frozen Lead Status fields. Stay warm!