When a commit is highlighted on the history list, when scrolling through a long list of commits, the commit history window will reset its scroll position to ensure that the currently-selected commit is visible in the window, meaning that the user has now lost the current scroll position, and must start scrolling down again to find whatever the user was looking for
STEPS TO REPRODUCE:
1. Open a Git repo in Source tree that contains a long history of commits.
2. Select a commit in the history list.
3. Scroll down a ways so that the selected commit is off screen.
4. Switch window focus to your favourite text editor. Make a change to a file currently tracked by the repo and save.
5. Switch window focus back to SourceTree.