I just checked it, I am shooting jpeg + RAW.

First shot drops to 8 or 9, and as fast as you can count to 12 it pops back up.
Here is the weird part. As soon as it hits 12 I take another shot. On the second shot it doesn't drop at all it stays at 12.
If I follow up with a third shot it will drop to 8 or 9 and as fast as you can count to 12 it pops back up.

Every other shot it drops to 8 or 9 and the next immediate stays at 12.

So I think what you have seen is the norm. FWIW I was in the house and was shooting at ISO 3200.