When clicking the Up button in the Documents & Media left navigational panel (Home, Recent, Mine, Basic Document etc) or the browser back button, currently the panel transitions to the new folder view by sliding them from right-to-left; as per Mika and Sergio, for consistency and intuitive UX reasons this transition should be from left-to-right instead.
Reproduce using the following steps:
1. Add the Documents & Media portlet to a new page
2. Add a folder "test1"
3. Enter folder "test1", and then click the back button; alternatively, click the Up button in the navigational panel