Staging files locks UI for long time, waiting for embedded git lfs

In my large git repository, which uses git-lfs for some files, SourceTree hangs for dozens of seconds every time I stage files. Looking at the task manager reveals git-lfs.exe maxing out the CPU while this occurs.

Also, the git-lfs.exe which is run is always the embedded version. However, I have it (also) installed in the system, and "use system git" is selected.

In contrast, unstaging is instant, as is staging in a repository without git-lfs.