That's exactly what happens. Additionally if the piston rings happen to line up just right when on the side stand more oil than otherwise might sleep past them. A couple of years ago I was really concerned when my RS smoked REALLY badly on start up. Learned on the forum what I described above probably happened and it never did it again like that.If you let your boxer sit on the side stand for a long period of time, some oil will leak down and get burned off when you crank it. Nothing to worry about but seeing some blue smoke when you're not expecting it might surprise riders.
On my GS1250 I do occasionally have a wee bit of smoke on startup and I'm sure that's why. I have about 5700 miles on her, she's going in for scheduled service and my oil level has dropped to the bottom line on the sight glass. I'm thinking that's normal given the above along with normal use.