I have found it works reliably if the issue is created via email request, or by the Help Center/portal.
However many tests have shown that adding via issues created by the green "create issue" button on the top of the queue, OR via "create linked issue" (which is what we really need this to work for).
I've set up a custom filter to add to the create issue screen to try to add them as the issue was created and that doesn't work either.