Subtask functionality not working

[hsbt]

Report from Martin J. Dürst

To make it a bit easier to move forward, I (thought I) created subtasks for https://bugs.ruby-lang.org/issues/12529.

These are the subtasks:
https://bugs.ruby-lang.org/issues/12549
https://bugs.ruby-lang.org/issues/12550

I created them clicking on 'Add' right to "Subtasks" on https://bugs.ruby-lang.org/projects/ruby-trunk/issues/new?issue%5Bparent_issue_id%5D=12529.

But the additional issues I created are not listed as subtasks under
https://bugs.ruby-lang.org/issues/12529, and don't list a parent issue.

If this feature doesn't work, I suggest removing the relevant part on the bug/feature pages. Otherwise, please fix it, or tell me what I did wrong.