many variegated plants like this buddleia will have sprouts that revert back to the parent green of the original species or cultivar. Keep in mind that many variegated plants are what can be classified as sports (spontaneous mutations) thus there variegations isn't always stable and if stressed the plant will have branches that revert back to the plan green. The best solution this type of problem is to first off remove all the green growth right down to the ground, second feed the plant as to relieve stress and hopefully prevent future reversion and finally take some cuttings of the variegated portions just in case the plant is unsaveable u can always start over.