I got the same issue as yours. I am using an iMac with a wired mouse. With the latest version of SL, I got an issue when I use "Object View" with Alt+Left hold click to zoom in and out, then my screen is spinning. I used to have this problem before around last month (older version). I tried deleting and downloading the viewer again. That time the issue has been solved. But this time, I tried the same way but still cannot fix it. I tried restart my Mac, delete the viewer and download again but the issue still happens. I think I should contact LL or submit a ticket to get support.