List of steps to reproduce:

• Make a comment and sign it with three tildes (~~~) instead of four, producing a signature without the timestamp.
• Add an "undated" template (like w:en:Template:Undated) after the signature with the timestamp that the comment was posted.
• View the comment.

What happens?:
There is no [reply] button after the comment.

What should have happened instead?:
There should have been a [reply] button after the comment.

Software version (if not a Wikimedia wiki), browser information, screenshots, other information, etc:
See my sandbox (permalink) for an example. I have added the magic word __NEWSECTIONLINK__ (used on discussion pages in non-talk namespaces) so that the "reply" links show.