On mediawiki.org, since this week, posting any reply to a LiquidThread message causes the message to disappear, although the message is posted.

Steps to reproduce:

1. Go to https://www.mediawiki.org/wiki/LiquidThreads_Test_Page
2. Reply to a message. Write a comment and hit the save button

Expected results:

• The message is added to the current thread, hiding the edit area

Actual results:

• The edit area disappears, and the message is not added to the current thread, although the message has been saved. Reloading the page displays the message.
• The error console displays an error:

		// Update reply links
		var threadWrapper = $( threadContainer ).closest( '.lqt_thread' )[0];
		var threadId = threadWrapper.id.substring( prefixLength );
                               ^

TypeError: threadWrapper is undefined lqt.js:630:6