Create a topic with "Title has {{foo}} in it" as the title.
In the same session, the placeholder text for a top-level topic reply becomes

Reply to "Title has  in it"

Now reload the board, or follow the Permalink to the topic. The placeholder for a top-level topic reply becomes

Reply to "Title has [[:Template:Foo]] in it"

It seems the progressive enhancement on the client is evaluating {{Foo}} as a handlebars template, while the server is evaluating it as wikitext. Both are incorrect, titles are plain text and should appear that way in the placeholder.

When you view the topic permalink, its HTML page <title> seems to have correct escaping of the topic title.

To reproduce both bugs, view http://en.wikipedia.beta.wmflabs.org/wiki/Talk:Flow so you see "This topic has ..." and "Another topic with..." posts, and then click to change the sort order.

Erik has a patch, gerrit 161101

Version: master
Severity: normal