I tend to follow the instructions when I work on my 1100S so when I pulled the front wheel to change the tire I came across incorrect info in the Ducati 1100 Workshop Manual as well as a parts schematic at Ducati of Omaha. Both diagrams show the wheel spacers in the reversed locations.
When I took the front wheel off I put the spacers on side of the bike from which they came, but when I read the manual to reinstall the wheel the exploded view showed the spacers reversed. I decided to try it as shown in the manual and the left disc hits the left fork so I put the spacers back in the correct locations - the thin spacer goes against the right fork, the wide spacer with the groove in the middle goes against the left fork.
I found a forum post about it in Aircooled, but it took me a while so I figured this would be a good Wiki item.