Oil locked motor

I have a 2005 fe450. Was grooving down a wash in 6th, not wrapped out, when I let up on the throttle then goosed it again. I heard a bang bang and the motor locked. As i was coasting to a stop I let out the clutch and got her to turn and start only to immediately die again. Once stopped I got it to light again and it smoked like the combustion chamber had filled with oil (SMOKE SCREEN). Got it lit and babied it out of the desert. Rode it about 15 miles, At the truck I checked for water in the oil and vice versa, nothing. Not overheated, seemed to run ok with a tiny bit of smoke. Dropped it off to the ony Berg dealer here to have it checked. They state that it has 50% leak down so I authirized a tear down. Both exhaust valves have lips, cylinder sleeve looks ok and piston isn't toast however as long as it's apart I'm going to do the top end. I'm just uncomfortable that nobody at the dealership can explain what may have happened to cause the oil to dump into the cylinder. I'm sure when it filled with oil it took out the rings but what caused it in the first place. Definitely don't want it to happen again! They also found a small sleeve laying in the bottom of the case and some copper fillings, scary part is they don't have any idea what it is or where it came from, they believe it is a clutch component but I've never had any cluch issues. Husaberg doesn't show it in the schematics and the dealer believes it may be a pressed in component somewhere!? HELP PLEASE!

Thanks bergbro, appreciate the heads up on the bushing. The oil thing has got me talking to myself! Wasn't sure if maybe there was some kind of breather that could have possibly dumped oil. The part thats got me stumped is it was like it hydrolocked but with oil instead of coolant. Very strange.

The valves weren't beat up, they have a small groove in the seat near the edge around the complete circumfrence, deep enough you can catch it with a fingernail. No damage on combustion side and no damage to top of piston. I don't know about the bearing material but makes sense to me that it would be copper based on my experience with automtive engines. Was wondering about that myself. I'm going by there today to do some more quizing and look closely at the damaged parts. Will be posting again later.I know that it didn't hydrolock but thats what it acted like.

Thanks for all the help and input.