A typical use of mirroring is where you have an outline of to-do items in various categories, and then mirror some of the items to a shortlist that can be re-ordered, e.g. in the order you’ll do things. But this doesn’t work as expected.
In this example, on the right “today list” side, you can move “wash dishes” up above “take out garbage” successfully. But if instead you move “take out garbage” down below “wash dishes” (not indented), then instead of having the same effect as expected, the mirrored copy of “take out garbage” will be moved to below the original location of “wash dishes” in “things to do”, so that there are two copies of “take out garbage” under “kitchen”, and “take out garbage” vanishes from the “today list”.
[edit: The moved item doesn’t need to be a mirror itself. If you add a non-mirror item to the “today list” above, and try to drag it below (not indented, just beneath) a mirrored item, it will be moved to the original location of the mirror in the “things to do” section.]
