Link to the uploaded document in RichTextHtmlField is not generated if custom document upload form is used

I have a RichTextHtmlField in a page. The user who is entering data need to upload the document for reference. I want to change the selected option of Destination Library in the form. To do so, I have copied entire content of Upload.aspx page and created a custom action to launch the custom upload form. When I click on the custom action button I am getting the exact ouput which I want but after the upload operation completes I am not getting the link generated in the field area, as SharePoint OOTB upload form does.

My custom action contains following code:

<CustomAction Id="Ribbon.PublishTab.Publishing.Actions.UploadDocumentButton" Location="CommandUI.Ribbon">
    <CommandUIExtension>
      <CommandUIDefinitions>
        <CommandUIDefinition Location="Ribbon.EditingTools.CPInsert.Links.Controls._children" >
          <Button Id="Ribbon.PublishTab.Publishing.UploadDocumentButton1"  Command="UploadDocumentButton1"
                  Image16by16="/_layouts/15/Solution/Images/Approval_16_by_16.jpg"
                  Image32by32="/_layouts/15/Solution/Images/Approval_32_by_32.jpg"
                  LabelText="Upload File" TemplateAlias="o1" Sequence="1000" />
        </CommandUIDefinition>
      </CommandUIDefinitions>
      <CommandUIHandlers>
        <CommandUIHandler Command="UploadDocumentButton1" CommandAction="javascript:function test(){

                          var url = _spPageContextInfo.webAbsoluteUrl + '/_layouts/15/DiscussionBoardEventReceiver/Pages/UploadFile.aspx?UseDivDialog=true&amp;LCID=1033&amp;Source=' + _spPageContextInfo.serverRequestPath +'&amp;AssetPageFolder=true&amp;seed=0.10343389471709208';                          
                          var options = {url: url};
                          SP.UI.ModalDialog.showModalDialog(options);                             

                          } test();">
        </CommandUIHandler>
      </CommandUIHandlers>
    </CommandUIExtension>
  </CustomAction>

The page UploadFile.aspx the exact code which is found in Upload.aspx in \_layouts folder.

The file is uploaded successfully but the link is not getting generated. What am I missing?