[wp-trac] [WordPress Trac] #49751: Old Featured Images (Thumbnails) Broken in 5.4

[WordPress Trac]

#49751: Old Featured Images (Thumbnails) Broken in 5.4
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 Reporter:  ispreview        |       Owner:  (none)
     Type:  defect (bug)     |      Status:  new
 Priority:  normal           |   Milestone:  5.4.1
Component:  Post Thumbnails  |     Version:  5.4
 Severity:  major            |  Resolution:
 Keywords:                   |     Focuses:
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Comment (by ispreview):

 I don't know if this helps, but during testing I went back to some of my
 very earliest posts from 2012 and opened one of them to Edit. I noticed in
 the 'Feature image' preview box (bottom right in classic editor) that the
 image wasn't rendered (it's the same on all of the affected posts). I
 uploaded a picture of what I mean by this here:

 http://www.mjon.co.uk/images/featured_image_missing.jpg

 No idea what version of NextGen Gallery was being used back then, but I
 guess it's whatever was the latest release at the time. I also decided to
 extract the HTML source code from that specific preview so you could see
 it (domain redacted):

 OLD Featured Image Preview Box Code

 {{{
 <div class="inside">
 <p class="hide-if-no-js"><a title="Set featured image"
 href="https://THEDOMAIN/wp-admin/media-
 upload.php?post_id=304&type=image&TB_iframe=1&width=753&height=941"
 id="set-post-thumbnail" class="thickbox"><img
 src="https://THEDOMAIN/index.php?callback=image&pid=669&width=&height=&mode=crop"
 alt="o2 uk" title="o2 uk" width="266"></a></p><p class="hide-if-no-js"><a
 href="#" id="remove-post-thumbnail"
 onclick="WPRemoveThumbnail('de085490c5');return false;">Remove featured
 image</a></p></div>
 }}}

 ..and then as an experiment I went to re-add the exact same feature image,
 albeit using the modern NextGen Gallery plugin, which produced this HTML
 code for the same preview box:


 {{{
 <div class="inside">
 <p class="hide-if-no-js"><a href="https://THEDOMAIN/wp-admin/media-
 upload.php?post_id=304&type=image&TB_iframe=1" id="set-post-
 thumbnail" aria-describedby="set-post-thumbnail-desc"
 class="thickbox"><img src="https://THEDOMAIN/wp-content/uploads/o2_uk-
 600x600.gif" class="attachment-266x266 size-266x266" alt=""
 srcset="https://THEDOMAIN/wp-content/uploads/o2_uk-600x600.gif 600w,
 https://THEDOMAIN/wp-content/uploads/o2_uk-800x800.gif 800w,
 https://THEDOMAIN/wp-content/uploads/o2_uk-768x768.gif 768w" sizes="(max-
 width: 266px) 100vw, 266px" width="266" height="266"></a></p><p class
 ="hide-if-no-js howto" id="set-post-thumbnail-desc">Click the image to
 edit or update</p><p class="hide-if-no-js"><a href="#" id="remove-post-
 thumbnail">Remove featured image</a></p><input type="hidden"
 id="_thumbnail_id" name="_thumbnail_id" value="21846"></div>
 }}}

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Ticket URL: <https://core.trac.wordpress.org/ticket/49751#comment:10>
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