My 1200 does the same thing especially if parked on a slope leaning left. I was told that the oil slowly gets past the rings into the combusiton chamber.
One time I left the bike on the side stand in my back yard (with a pretty steep slope) for 4 days. when I started it I thought that I had blown the engine up somehow. After a short warm up, it wuit smoking.
when i bought my 86 it had sat for a while and took 1/2 hr to clear...people thought the neyborhood was on fire...i was shocked and seller was laughing said to wait...they all do it
rode it for 10 yrs with no probs and no smoke...but they should not smoke overnight or short term downtime...valve seals need doin
I have found that if I keep my oil level at the lower mark on the view window it eliminates the smoking at start up after parking on the side stand. I also avoid parking where the ground slopes away to the left.