Why is my pump pressure rising when filter is engaged...but there's nothing inside the DE filter?

I'm baffled. My Hayward Superpump and MPV, when set to filter as brand new without adding DE showed a pressure of 10psi. So that's baseline with a water path impeded only by empty grid fabric. Adding DE brought the psi up to maybe 11 or 12. So that's a more useful baseline. Later, I was experiencing higher pressure AFTER backwash, 15 to 17; even after multiple backwash/rinse cycles and clear water, I couldn't get the pressure below 15 psi. So here's the weird part: I removed the filter grids...

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