I am experiencing a reproducible issue when performing the following sequence of actions.
1. In a Jira issue with multiple subtasks, reorder them by dragging and dropping.
2. Then update the summary by pressing the pencil-shaped button to the right of the subtask.
As soon as the summary is updated, the subtasks go back to their previous order. (before step 1)
When you refresh, they're back in the order you intended in step 1 (after step 1).
It's a minor bug, but I think it can cause more confusion than you might think.
Thanks.