Hi! Trying out a trial of Balsamiq Mockups 3.5.5 on macOS Sierra (10.12.2) on a 2015 iMac with the Apple Magic Trackpad 2 (that’s a mouthful).
I noticed when choosing a category in the UI Library on top (“Assets”, “Big”, etc…) and scrolling through it with the trackpad, the scrollbar/elevator will get stuck all the way to the right, and then scrolling back and forth will start spamming the UI Library with duplicate elements (which gets worse the more you try scrolling). I’ve attached a picture of what I’m talking about:
This happens both when scrolling left/right on the trackpad, or using the “SHIFT+vertical scroll” trick. Interestingly enough, it does not seem to happen on the “All” list in the UI LIbrary, so I’ll be sticking with that for now. Hope this is reproducible - let me know if you need more information.