moving children

[dspady]

When I move a child topic to the left the topic moves to the bottom of what could be a long list. Why does it not go immediately to the left and immediately below its former parent. For example:
x (parent)
/ y (child)
x (some other child's parent)
x
Move y one column left and you get
x
x
x
y (the former child is now here)
instead of
x
y (former child)
x
x