Problem description: 
Shift-Up/Down stops on hidden cells

Steps to reproduce:
1. cells A1=Header, A2=1, A3=empty, A4=1
2. enable filter by Header=not empty
3. select A2
4. click Shift-Down and nothing happen
5. click Shift-Down for select A2:A4

Current behavior:
Shift-Up/Down stops on hidden cells

Expected behavior:
Shift-Up/Down/Left/Right must skip all hidden cells.
1. cells A1=Header, A2=1, A3=empty, A4=1
2. enable filter by Header=not empty
3. select A2
4. click Shift-Down once for select A2:A4

Platform (if different from the browser): 
Ubuntu 11.10

Browser: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:11.0) Gecko/20100101 Firefox/11.0