Mislabeled Death Star Bags

Dougout

Soooo I got up to Step 6 yesterday with the Death Star (I have been a bit slow) and I discovered there were only 3 bags which were far too small to build the whole step. Looking for the other bags, I opened up the last inner box and it contained only Step 7 bags. I was certain there was no missing legos because I had weigh checked the set and all the inner boxes were fully packed, so I searched around a little and realized about half the parts for Step 6 were in Step 7 bags.

In my picture you can actually see the window piece that is exclusive for Step 6 in the wrong bag. Also, the tall (6 brick high) cylindrical pieces that go in the middle of the DS are visible in the Step 7 bags. I thought this was quite odd to have incorrectly labeled bags as I have never come across this before. If I remember correctly, those 2 bags came in the inner box with the other Step 6 bags, so they were placed in the right box, only labeled wrong. Anyone know if this is a common occurrence or is it rare for the factory to screw up a bit?