I have seen this issue mentioned on other forums with the JD 620i model (tractorpoint.com). Not sure if anything changed with the 625i design. Some Kawasaki Mule owners have also complained of gas in the oil too. The general consensus on why this happens has to do with the electronic fuel injection system not having a sophisticated enough efi sensor to lean the fuel mixture before the engine reaches operating temps. Some corrective helpful solutions from owners vary from running hotter rated spark plugs to adjusting the air/fuel mix leaner to blocking the radiator with cardboard in an effort to get the engine to warm up quicker.