ok,
what i've done when i have that problem may not be the right thing, cause i have no idea why it happens, but it works and is simple.
In the movie that brings that menu (form the ? mark), add another key frame at the end of each icon layer, then in this frame, place the icon directly from your library and align it in the same position as the others.

I find it is conmon that a button won't work when is not in the main timeline after is being animated.
hope this helps