My RCBS does the same thing sometimes. Then I clean it again making sure to get the dust out of the grooves of the balance point and its ok again. You're scale just needs a spring cleaning.
"Always place your clothes and weapons where you can find them in the dark"
"Understand that the enemy is not the enemy in his own eyes ;this may offer you an opportunity to make him your friend. If not, you can kill him without hate, and quickly."