I can confirm (happend to me several times), but I wasn't able to tackle it down yet.

Sorry, Please ignore the above commit message. I was trying to give demo for next PBF14.
Thanks.

If you look at the requests, IE actually does the request twice for some reason:

While Chrome only does it once as expected:

At least it explains why we get it duplicated. However I don't know why the request is fired twice.

When I enable debugger on IE.
I get a error on cancel (modal), I think its a different issue, but maybe its the same?

<button class="btn" type="button" onclick="document.id('batch-category-id').value='';document.id('batch-access').value='';document.id('batch-language-id').value='';document.id('batch-tag-id)').value=''" data-dismiss="modal">
Cancel </button>

Unable to set property 'value' of undefined or null reference

I can't confirm the issue with a menu item, but I can confirm it with Contacts.

This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/4511.

Issue also confirmed from me.
Tested with menu item and it did copy it 2x

System information:
Joomla! 3.3.6 - IE11

This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/4511.

Okay, here is what I could find out so far, but I have no idea how to continue. (I'm testing with contacts as I get the issue there and not with menus).
Once we click on Process we send just one request to the site. The type of the request is POST, it calls index.php?otpion=com_contact. The body of the request is absolutly the same as with all browsers I checked (ff, chrome). The issue however is the redirect that we do in our ContactControllerContact in the batch function. We do a 303 redirect (see other) and for some reason instead of doing a GET request (as per HTTP 1.1 specs) IE does POST request with the same data that we had in our first request... The second post generates the second copy of the item.
Other people have also experienced this:
https://social.msdn.microsoft.com/Forums/ie/en-US/92c769c3-e359-4b0c-8111-420021466d0f/redirect-request-on-ie-from-a-post-request-302303-is-also-having-the-request-method-as-post-and?forum=iewebdevelopment

Either it is a bug in IE11 and we can't do anything about it, or it is still a bug with IE11, but we could do something in our code to go around the issue?

Any ideas?

This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/4511.

It may be related to the fact that we create different redirects for IE than for other browsers. See https://github.com/joomla/joomla-cms/blob/staging/libraries/joomla/application/web.php#L518
I discovered once that long ago.

It has been over a year since the last comment on this issue. Can anyone still replicate this with the current release of Joomla or has it been resolved elsewhere?

The bug is still there.

J35B1
Win10 IE11, also on Edge

Thanks for confirming - setting status back to confirmed

I can also confirm the issue still happens, both in IE11 and Edge (On Windows 10)

Bug still exits on Win 8.1 IE 11 & Edge and on Win 10 IE 11 & Edge

ok, now I'm getting some errors on the staging build:

Warning: Header may not contain more than a single header, new line detected in C:\wamp\www\develop\libraries\joomla\application\web.php on line 959

Error

An error has occurred.

1062 Duplicate entry '0-1-xwsxw-2-' for key 'idx_client_id_parent_id_alias_language' SQL=INSERT INTO #__menu (parent_id,level,lft,rgt,alias,id,menutype,title,note,path,link,type,published,component_id,checked_out,checked_out_time,browserNav,access,img,template_style_id,params,home,language,client_id) VALUES ('1','1','137','138','xwsxw-2','0','mainmenu','xwsxw (2)','','xwsxw','index.php?option=com_content&view=article&id=1','component','1','22','0','0000-00-00 00:00:00','0','1',' ','0','{\"show_title\":\"\",\"link_titles\":\"\",\"show_intro\":\"\",\"info_block_position\":\"\",\"show_category\":\"\",\"link_category\":\"\",\"show_parent_category\":\"\",\"link_parent_category\":\"\",\"show_author\":\"\",\"link_author\":\"\",\"show_create_date\":\"\",\"show_modify_date\":\"\",\"show_publish_date\":\"\",\"show_item_navigation\":\"\",\"show_vote\":\"\",\"show_icons\":\"\",\"show_print_icon\":\"\",\"show_email_icon\":\"\",\"show_hits\":\"\",\"show_tags\":\"\",\"show_noauth\":\"\",\"urls_position\":\"\",\"menu-anchor_title\":\"\",\"menu-anchor_css\":\"\",\"menu_image\":\"\",\"menu_text\":1,\"menu_show\":1,\"page_title\":\"\",\"show_page_heading\":\"\",\"page_heading\":\"\",\"pageclass_sfx\":\"\",\"menu-meta_description\":\"\",\"menu-meta_keywords\":\"\",\"robots\":\"\",\"secure\":0}','0','','0')

Warning: session_write_close(): Failed to write session data (user). Please verify that the current setting of session.save_path is correct (C:/wamp/tmp) in C:\wamp\www\develop\libraries\joomla\session\handler\native.php on line 192

Hi @810! You created this issue sometime ago but have not provided any code for people to evaluate. As no one else has shown any interest in providing the code and you have not, then I am closing this issue at this time. If code is provided (a pull request) it can always be re-examined. Thank you!