'Add Comment' redirects to a new page and add attachment button disappears when clicked

Issue Summary

In JSM Project, when user clicks on Add comment, it takes user to new link. The issue is observed in JSM 5.x version.

This is reproducible on Data Center: (yes) / (no): Yes

Steps to Reproduce

1. Disable service-desk-comment-field module under Jira Service Management plugin.
2. Open a JSM Ticket
3. Click on 'Add comment'
4. It is redirected to a new page (Url) with only comment section showing up in the page.

Expected Results

When Clicked on 'Add Comment' it expands the comment section in the same page (url) and attachment button should give user option to select file and 'Upload'

Actual Results

When Clicked on 'Add Comment', it is redirected to a new page (Url) with only comment section showing up in the page and when click on Attachment button it disappears.

Workaround

Change 1

Enable the comment on the issue view page

Location:
atlassian-jira/WEB-INF/classes/templates/plugin/comment/addcomment.vm

Before:

#enable_html_escaping()
<div id="addcomment" class="module#if($isStickyCommentEnabled) sticky#end" data-sticky-comment-enabled="${isStickyCommentEnabled}">
    ${commentHtml}
    #if($shouldAttachAddCommentEventHandler)
        <jira-create-comment-form></jira-create-comment-form>
    #end
</div> 

After:

#enable_html_escaping()
<div id="addcomment" class="module#if($isStickyCommentEnabled) sticky#end" data-sticky-comment-enabled="${isStickyCommentEnabled}">
    ${commentHtml}
    <jira-create-comment-form></jira-create-comment-form>
</div>

Change 2

Keep the popup in the same position

Location:

atlassian-jira/includes/ajs/layer/InlineLayer-min.js

Before:

scroll:function(){this.setPosition()}

After:

scroll:function(){if(this.$content[0].id === "commentLevel"){return};this.setPosition()}