Is it possible that when the valve cover was removed, the oil spilled outin areas that you didn't get cleaned up and you are seeing the oil burn off? If the seal isn't leaking- no big deal. If it is, get the same color. So if the oil level is set properly (used 10w-30 I presume)and the foam filter isn't over oiled- you may get the privelige of replacing head gaskets....

Did you tip the machine up on one side when servicing? Sometimes oil will get into the intake tract and muffler when doing so and may take a few minutes to burn off. I don't see anything else in what you did that would cause sudden oil-burning, unless there's too much oil in the crankcase. I think filter oil is great for the pre-filter, but too much of any oil will migrate to the paper filter causing restricted air flow and a rich condition which will sometimes cause blue/black smoke as the excessive fuel 'washes' oil off the cylinder wall.
Also, just by chance are you storing it differently after use than before the service, so that it's not level?

try replacing your pre-filter (don't oil, leave dry).also are you sure you did'nt overfill crankcase. dave

Where is the bluish/white smoke coming from.