Welcome, and don't be freaked out: There are two common causes of oil puking out of 750s:
1) It has been over-filled. The oil is held in the tank by a check valve. These leak the oil out of the tank over time, so if you check the level after the bike has been sitting, it appears low, and you add oil. After the bike gets started, the oil in the sump gets pumped back into the tank, and it overflows out the vent.
2) The drain from the oil-separator built into the oil tank (the lower spigot on the tank) is not plumbed to the spigot at the rear of the transmission.