Comment 5 for bug 619156

I don't understand, it's the default behaviour with Ubuntu on 3 different computers.
I searched the code for you, I think it's here : http://git.gnome.org/browse/nautilus/tree/libnautilus-private/nautilus-horizontal-splitter.c
It's a HPaned which can resize from the left component size to 0 and save old size (splitter_collapse function) and the opposite from 0 to the saved size (splitter_expand function).
I think you probably delete the ScrolledWindow, so the HPaned can just collapse to the TreeView minimum size.
Maybe I am wrong, but the code seems to follow my behaviour.

(Sorry if my english is bad)