Without seeing the bike, I would guess that this is the crankcase vent. Originally, the crankcase vent tube came up from behind the oil pump and went to the backside of the air filter. A lot of owners changed the routing of this hose due to oil being blown into the air filter. They simply remove the metal part of the tube and replaced it with a short open ended hose running back and ending just forward of the rear tire.
As for the oil blowing out of the tube, it depends on how much oil blows out of the tube. If it's just a mist that will sometimes coalese into a droplet, this is about normal. But, if it's a steady drip or flowing oil, this is not right.
If the mist is heavy, this could be caused by excessive blowby on the rings creating high crankcase pressures. The use of synthetic oil should not increase the blowby unless the rings are in poor shape, then it will. The use of synthetic oil seems to aggrevate any minor leak turning it into a much larger leak.
If the oil is coming out in a steady stream or pumping the oil out of the engine, you proabably have sheared a key in the scavenge gears of the oil pump and it's not pumping the oil back into the oil tank.
Now there is a vent hose on the oil tank but it should be routed to a fitting on the crankcase that is located just above and slightly behind the top of the oil pump.
Good Luck
Steve
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