2 hanging candelabra style lum-inaires, each with three 40w bulbs...

owner says have always been dim since house was built... today a bulb burns out in the upper lum. and the other 2 bulbs in that lum. get brighter, at the same time the other 3 bulbs in the lower lum. get dimmer. so they put a new bulb in the upper lum. and the 2 lum's balance out as before... both lum.'s revert to being as equally dim as they have always been

so, they tested it...
they screw the 3rd bulb into the upper lum., and the lum.'s are equally dim, all 6 bulbs dim.
then they unscrew that 3rd upper lum. bulb and the other 2 upper lum. bulbs get brighter, and the 3 lower lum. bulbs get dimmer

is this obvious to the most casual observer? i bet its really easy and i'm going to be embarrassed [again] ;-)