And they happen in all classes. I had a situation with Delta Airlines where I pre-selected First Class seats for my son and I (him window and me aisle) on the same PNR by the way. On check-in I was re-assigned the aisle seat in the row behind! As a matter of interest I asked the guy who got my seat if he had specifically requested it. He replied not at all. So we did a swap and all was resolved. However, why the heck did that happen in the first place?