There was a response back to a similar issues for AC14 with MACs and a second screen.
I was getting an 'auto' scroll to the right on AC19 when using the explore mode, I pulled my AC19 to the second screen and activated explore mode and it fixed the 'auto' scroll issue.
It appears to be a graphics/screen related issue an not a mouse issue.
I'm running a AMD FirePro v3900 on a Gigabyte MA78LMT-S2 motherboard with Phenom II 955 CPU, with 2 LCD panels on the GPU (if that helps?!).
It appears that there has been an issue with the 'explore' mode in various guises going back to AC14.