Hi I can't say if the bike being laid over could cause the oil to pour out as you describe but how's the oil level in the tank ,have you had to top it up recently if so and the sump had more in than normal it could have vented into the chaincase and with the bike laid over it's leaked out of the filler cap .However,that would mean that you've acheived the near impossible ,getting the chaincase completely oiltight in the first place .I can't wait to see what cleverer people than I think ,should be interesting ,best of luck BobH.