[messaging-app] selection toggle doesn't unselect items in main view

steps to reproduce
build r172

1. launch messaging app, make sure your landing view has several conversations stored
2. long press on any list item
3. check boxes appear next to the list items and you should be able to select them individually (try it out)
4. now tap the "box + tick" icon in the header to select all items at the same time
5. tap it again

Actual result:
The 2nd tap on the "box + tick" icon in the header does not unselect all list items as though. Ideally the icon in the header should toggle:
a) square with tick = select all
b) empty square = unselect all

----------------UX comment---------------
Expected result:
As you were able to select all items with one tap on the "box + tick" icon, a second tap should unselect them

Currently it works correctly in the Address Book and Phone app, apart from changing icon in the header.