They do that with side signals, not with mid. If you get bad center, it's different frequency response between two drivers, aka driver imbalance.

That's the beauty of my K612 - they sound spacious and they have great imaging because of epic center - all at the same time. I can name my Shure SRH840 as being the opposite - less spacious and very bad center (bad batch - channel imbalance is too high).