Mother bunny acting strange?

My mother bunny just had her 3rd litter of healthy babies. We noticed last night she had taken 2 of the babies and thrown them out of the nest and her hutch all together. The hutch is pretty big and high off the ground(about 4 feet). She had to open her door the oppsite way (inward) and actually throw them out onto the ground. We found them and they were warm and squirming. We put them back with the others in the nest and checked on them throughout the night. Seemed fine. Is this normal behavior? Why would she only throw out 2 of the 6?