Steps to replicate the issue:

• Go to any WMF wiki.
• Go to Special:Preferences on that wiki and enable the "Show preview without reloading the page" option, under the "Editing" tab.
• Open any page for editing on that wiki, using the 2010 wikitext editor.
• Type an edit summary.
• Click "Show changes".

What happens?:
The preview of the edit summary does not appear under the edit summary box.

What should have happened instead?:
The preview of the edit summary should appear under the edit summary box, as was the case before 1.41.0-wmf.15, and as is still the case when the "Show preview without reloading the page" preference is disabled.

Other information:
This bug is new to 1.41.0-wmf.15, and possibly has to do with e74787644d150d27d98d211a1176d219cdd8c42e. While the edit summary preview does appear when clicking "Show preview", it should appear when clicking "Show changes", too. This is how it's always been, and this is the correct behavior: Often one doesn't need to preview their changes, but still wants to review what was changed in their edit. It is convenient to see a preview of the edit summary in such cases, particularly when the summary is long and includes links.