There have been a few discussions on this, and the behavior is normal. The workaround is to not close the card slot door - open the door, pull a card, insert a new card, then close the door. When you close the card door, even with the camera 'off' you'll notice that the card activity light flashes. It's set as the default behavior to avoid recording to an empty slot. My 1D X does the same thing.
If this is happening without closing the card door, that's not normal AFAIK.