Probably loose screws on the handle, or slight variations in the mounting position, or maybe the screws holding the display assembly to the player casing are loose and/or the positioning of the various bits is slightly shifted. Various bits that connect the player to the sled (docking connector, guide bumps) could be working tighter than before. Sled frame could have been bent slightly to cause this. Also, the squarish bits on the back of the handle could simply be wearing down.

Rob is right, the player was never intended to do that, and it's something that doesn't happen to every player. On my player, I get a slight rub-marks at the friction points, but not an actual ejection motion.