does anyone think that maybe the bahrag , when they were beaten , where locked ...   ... in the hearts of the toa themselves ?
this would make sense as the toa are now only powerfull when they are close together , as the bahrag and the only way to free them would be to retreave the nuva cube parts from the toa . this would explain the bohrok kal as being a fail safe mechanism incase this happened , designed by the bahrag  

maybe there stuck in a hole. (in the cell)