The easiest way to test if modified-hildon-desktop is active is by checking if left/right arrows switch desktops in the home screen, as this feature is not configurable.

I don't think an update might have caused problems, since PR1.1.1 did not update the hildon-desktop package, and modified-hildon-desktop could not be installed prior to PR1.1.

Setting ctrl_backspace_in_tasknav to 3 does not give you alt-tab like behaviour. See description of the possible values here:
http://my.arava.co.il/~matan/repo/Mo...n_Desktop.html