Code review comment for lp:~mc-return/compiz/compiz.merge-fix1082001-gridded-windows-jump-workspaces

I don't have any code to show as I just checked what wall did but expo didn't. As DnD fails, I assume you're emitting those events right when expo starts/quits(?). If you emit the events only when expo calls moveViewport, it shouldn't affect DnD windows (emitting those events equals to situation without grid). So something like this could work:
  screen->handleCompizEvent ("expo","start_viewport_switch", CompOption::Vector());
  screen->moveViewport(...)
  screen->handleCompizEvent ("expo","end_viewport_switch", CompOption::Vector());

I don't have time to test it right now, but I can try it later...