UPDATED: Final implementation of CustomWorkboxFrom looks like above:

using System;
using System.Collections.Generic;
using System.Linq;
using Sitecore;
using Sitecore.Text;
using Sitecore.Web;
using Sitecore.Workflows;
using Sitecore.Workflows.Simple;

namespace Test
{
    public class CustomWorkboxForm : Sitecore.Shell.Applications.Workbox.WorkboxForm
    {
        /// <summary>Gets or sets the offset(what page we are on).</summary>
        /// <value>The size of the offset.</value>
        private OffsetCollection Offset = new OffsetCollection();


        /// <summary>Refreshes the page.</summary>
        protected override void Refresh()
        {
            this.Refresh(null);
        }

        /// <summary>Refreshes the page.</summary>
        /// <param name="urlArguments">The URL arguments.</param>
        protected new void Refresh(Dictionary<string, string> urlArguments)
        {
            UrlString urlString = new UrlString(WebUtil.GetRawUrl());
            urlString["reload"] = "1";
            if (urlArguments != null)
            {
                foreach (KeyValuePair<string, string> urlArgument in urlArguments)
                    urlString[urlArgument.Key] = urlArgument.Value;
            }

            var url = WebUtil.GetFullUrl(urlString.ToString());
            var uri = new Uri(url);
            var clean = uri.GetComponents(UriComponents.AbsoluteUri & ~UriComponents.Port,
                UriFormat.UriEscaped);

            Context.ClientPage.ClientResponse.SetLocation(clean);
        }

        /// <summary>
        /// Workflow completion callback to refresh the counts of items in workflow states.
        /// </summary>
        /// <param name="args">The arguments for the workflow execution.</param>
        [UsedImplicitly]
        private void WorkflowCompleteStateItemCount(WorkflowPipelineArgs args)
        {
            IWorkflow workflowFromPage = GetWorkflowFromPage();
            if (workflowFromPage == null)
                return;
            int itemCount = workflowFromPage.GetItemCount(args.PreviousState.StateID);
            if (PageSize > 0 && itemCount % PageSize == 0)
            {
                int num = Offset[args.PreviousState.StateID];
                if (itemCount / PageSize > 1 && num > 0)
                    Offset[args.PreviousState.StateID]--;
                else
                    Offset[args.PreviousState.StateID] = 0;
            }
            Refresh(workflowFromPage.GetStates().ToDictionary((state => state.StateID), (state => Offset[state.StateID].ToString())));
        }


        private class OffsetCollection
        {
            public int this[string key]
            {
                get
                {
                    if (Context.ClientPage.ServerProperties[key] != null)
                        return (int)Context.ClientPage.ServerProperties[key];
                    UrlString urlString = new UrlString(WebUtil.GetRawUrl());
                    int result;
                    if (urlString[key] != null && int.TryParse(urlString[key], out result))
                        return result;
                    return 0;
                }
                set
                {
                    Context.ClientPage.ServerProperties[key] = (object)value;
                }
            }
        }
    }    
}

Unfortunately, if you still want to remove the port from URL, you need to include some implementation of private method defined in base class.

You can create your CustomWorkboxform class and inherit it from the 'WorkboxForm'. The try to override protected new void Refresh(Dictionary<string, string> urlArguments) method (using new keyword as this method is not virtual). Then you will have to update Workbox.xml with new CustomWorkboxForm code behind implementation (\sitecore\shell\Applications\Workbox\Workbox.xml). There can be some another difficulties with overlapping other methods. But idea might work!

You can create your CustomWorkboxform class and inherit it from the 'WorkboxForm'. Then try to override protected new void Refresh(Dictionary<string, string> urlArguments) method (using new keyword as this method is not virtual). Then you will have to update Workbox.xml with new CustomWorkboxForm code behind implementation (\sitecore\shell\Applications\Workbox\Workbox.xml). There can be some another difficulties with overlapping other methods. But idea might work!