I can create articles as a sub-articles of another article, but when I want to move an article, only categories are listed as targets.

1. Create a category A
2. Create an article B under category A
3. Create an article C under category A
4. Create an article D under article B
5. Try to move article D
6. You'll see you can only move article D to category A (or none), not to article C, or even its current position of B is not a valid place you can move it to.