Thread:Extension talk:LiquidThreads/Threads added to /wiki/API without subject line

We have the problem that any threads that are being created using LT, but where no subject is defined are ending up on /wiki/API instead of the designated Talk: page. We're using r75373 of the development trunk with a 1.16.x mw installation. Is a more recent revision still working with mw 1.16.x ?

Here's how one of our users described the problem in his ticket:

When "starting a new discussion" on a Talk:Title page and omitting the "subject" text entry cell, the resulting discussion (without threading or signature) is saved @ https://www.hackerspace.lu/wiki/API instead of the Talk:Title page.

I haven't verified the version used on mediawiki.org but on here, threads are not allowed without a subject line. I can't find any reference to making fields obligatory on the extension's manual page. Thanks for your help!