RichHtmlField showing html markup in display mode

Sorry for replying with answer after long time. I wondered when I saw there is no answer to this question. So decided to do self-reply to this question. After lots of brain storming I get to know there was silly mistake I did in feature receiver. When I debug application I come to know that I was getting null values from site column properties. Then I placed null check condition on site column property values.

 public override void FeatureActivated(SPFeatureReceiverProperties properties)
            {
               List<string> htmlFields = new List<string> { "LunchBody","ContactInformation", "RegionsField", "SummaryLinksTools",
                        "OperatingSystemList" };

               if (properties != null)
                    {
                        SPSite currentSite = properties.Feature.Parent as SPSite;
                        SPWeb rootWeb = currentSite.RootWeb;
                        //Update site column in site collection
                        UpdateSiteColumns(htmlFields, rootWeb);

                        foreach (SPWeb childWeb in currentSite.AllWebs)
                        {
                            try
                            {
                                //Update pages library for each site.
                                UpdatePagesList("eNetContactInformation", childWeb);
                            }
                            finally
                            {
                                if (childWeb != null)
                                    childWeb.Dispose();
                            }
                        }

                    }
        }

private static void UpdateSiteColumns(List<string> htmlFields, SPWeb web)
        {
            foreach (string fieldName in htmlFields)
            {
                UpdateSiteColumn(web, fieldName);
                web.Update();
            }
        }

private static void UpdateSiteColumn(SPWeb web, string fieldName)
        {
            SPFieldMultiLineText fld = (SPFieldMultiLineText)web.Fields.GetFieldByInternalName(fieldName);
            string richTextValue = fld.GetProperty("RichText");
            if (!string.IsNullOrEmpty(richTextValue))
                fld.RichText = true;

            string richTextMode = fld.GetProperty("RichTextMode");
            if (!string.IsNullOrEmpty(richTextMode))
                fld.RichTextMode = SPRichTextMode.FullHtml;

            fld.PushChangesToLists = true;
            fld.Update(true);
        }

So this way we can update the site level columns through VS code.

However we can do same thing with the script as mentioned in question itself. It was running successfully but I was checking with wrong SharePoint site. Below powershell script is ok.

$site = get-spsite -limit All | where-object {$_.Url -eq "http://intra.******.enet"}



Write-Host "Vishal Processing Site Collection:" $site.Url
     foreach($web in $site.AllWebs)
   {
      Write-Host "Web:" $web.Url
       if($web.Url -like "http://intra.*****.enet/about/regions")
       {
         $list = $web.Lists["Pages"]
         [Microsoft.SharePoint.Publishing.Fields.HtmlField]$field =   [Microsoft.SharePoint.Publishing.Fields.HtmlField]$list.Fields.GetFieldByInternalName("eNetContactInformation")
         $field.RichText = $true
         $field.RichTextMode = [Microsoft.SharePoint.SPRichTextMode]::FullHtml
         Write-Host "Field: " $field.Title
         $field.Update()
         Write-Host "List: " $list
         $list.Update()
        }
    }