If your crank case is overfilled (either with oil or gas/oil mixture as in the case of a sticking float) It is possible that air would escape if the piston was on the downstroke at shutdown. The filler cap would be a high point, trapping air.
Other reasons include a clogged or capped off crankcase vent.
Check your airbox. If it's full of oil you have issues to deal with before you run the bike.