I have considered moving threads->detach() on a separate line before I made my original post though, but moving detach on to another line is not doing what you think it's doing. The following codes are not equivalent:

threads->create(\&create_threads, "param")->detach();
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and

threads->create(\&create_threads, "param");
threads->detach();
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In the first example, detach() is performed on the object returned by threads->create(), which detaches the thread created. Moving detach() on a separate line does not detach the thread at all, calling threads->detach() separately has no effect on the thread you just created.

The proof? Well, there is a threads->list() function that lists all non-joined, non-detached threads. Add threads->list() after threads->detach() showed that the created thread did not get detached at all.

I agree there is definitely a bug with detach() on out of scope object, but moving detach() on a separate line is not a fix. You must call $thread_created->detach() to truly detach the thread.