BC Optimus seems to have a design flaw that prevents almost all figures I have come across, from being able to work properly. Either the pop-up section doesn't stay down, or it doesn't release when the bumper is hit.
The one I ended up buying is in the first category, in that it doesn't stay down too well, unless I slam it in really hard for the tabs to catch and hold.
Just keep looking for one that works best I guess.