Weird keyboard problem Latitude D820

I'm having a very strange problem with the keyboard on a Latitude D820. The keyboard works, except for 6 keys, including B,N,?,Space Bar, and Ctrl and Alt on the left side. I replaced the keyboard with a BRAND NEW keyboard, and I'm having rthe EXACT SAME problem! The same keys don't work. If I use a USB keyboard, the USB keyboard works fine.

I ran all Dell Diagnostics - it's showing everything fine except for a problem with Serial Port 1. Does that have anything to do with the keyboard? The keyboard controller tested fine.

Is it possible I could have gotten 2 defective keyboards with the exact same defect? Has anyone else ever had this problem?

Any help would be greatly appreciated!

Thanks!