Imagine you have rows 0-8. You create a fold at row 0 with the following 5 rows. Then you create a fold at row 1 with 3 following rows. Rows 2, 3, and 4 are now children of both row 0 and row 1. Really, when a row gets becomes the child of a deeper-nested row, it should stop being a child of its previous parent, otherwise expanding 0 also expands all of the rows that are now nested under 1.
Imagine you have rows 0-8. You create a fold at row 0 with the following 5 rows. Then you create a fold at row 1 with 3 following rows. Rows 2, 3, and 4 are now children of both row 0 and row 1. Really, when a row gets becomes the child of a deeper-nested row, it should stop being a child of its previous parent, otherwise expanding 0 also expands all of the rows that are now nested under 1.