You may have an addon interfering somehow (unless you were trying to drag during combat?).
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"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh
Check in the interface menu as well. If i recall correctly, they have a checkbox for preventing moving icons. I found it turned on when I first logged on after the patch.