When setting the frontend.checkout.postcoderequired configuration setting to require the Postal Code, Kartris correctly requires that an entry is made but doesn't update the label to visually indicate it is a required field...
I'd suggest changing the CustomerAddress.ascx.vb file, at line 72 to the following:
If KartSettingsManager.GetKartConfig("frontend.checkout.postcoderequired") = "y" AndAlso value = True Then
valZipCodeRequired.Enabled = True
lblPostcode.CssClass = "requiredfield"
Else
valZipCodeRequired.Enabled = False
lblPostcode.CssClass = ""
End If
This fixes the issue so that the label visually indicates it as a required field based on the configuration setting.