[CONNECT C#] - Issue with TagElement.ReplaceInModel(null)

I'm trying to update the URL for Engineering Links in a collection of DGN files. The problem is that I seam to be creating duplicates of the TAG when writing the updated element back into the model.

After processing a file, following the engineering link still takes you to the old address and not the new one.

/// <summary>
/// Scans model looking for tag elements processing them withScans model looking for tag elements, processing them with 
/// <see cref="TagElementProcessor(Element, DgnModelRef)"/>
/// </summary>
/// <param name="model">The model to scan</param>
private void UpdateEngineeringLinks(DgnModel model) {
    var criteria = new ScanCriteria();
    var elementTypes = new MSElementType[] { MSElementType.Tag };
    var status = criteria.Scan(TagElementProcessor);

/// <summary>
/// Call back method for UpdateEngineeringLinks model scan. <see cref="Bentley.DgnPlatformNET.ScanDelegate"/>
/// <para>
/// If the element is an internet url tag, get the current value and then use <see cref="UpdateValue(string, out bool)"/>
/// to perform a replace of the matching part. Then if updated, set as the new value for the tag.
/// </para>
/// </summary>
/// <param name="el">The current element that matches the scan criteria</param>
/// <param name="modelRef">The model</param>
/// <returns></returns>
public StatusInt TagElementProcessor(Element el, DgnModelRef modelRef) {
    if(el.ElementType == MSElementType.Tag) {
        var model = modelRef.GetDgnModel();

        if (model.IsReadOnly) {
            return StatusInt.Error;

        TagElement tagElement = (TagElement)el;
        if(tagElement.TagSetName.Equals( "internet", StringComparison.InvariantCultureIgnoreCase)
            && tagElement.TagName.Equals("url", StringComparison.InvariantCultureIgnoreCase)) {

            var oldValue = tagElement.GetTagValue().ToString();
            var newValue = UpdateValue(oldValue, out bool updated);

            if (updated) {
                LogDetails.AppendLine($"Updating Engineering link {tagElement.TagName} from '{oldValue}' to '{newValue}'");
            } else {
                LogDetails.AppendLine($"Skipping Engineering link {tagElement.TagName} with value '{oldValue}'");

            return StatusInt.Success;

    return StatusInt.Error;

Am I missing something? (easily done given the poor quality of the API documentation).