Working on Windows 7 64bit with following software versions:
Git for Windows 2.8.3
SourceTree 1.8.3.0

Context:

• looking at a commit in the 'Log / History' tab
• the commit has many changed files (~200 files)

Triggering actions:

• click the first file in the list of changed files for that commit
• press and hold the 'arrow down' key to go down the list of files

The last action spawns a 'git.exe' process for every file, which in turn spawn a 'git-log.exe' process.
One would expect these 'git-log.exe' processes to end or be killed by SourceTree.
Instead, these processes lose the parent/child relationship with the Git and SourceTree process and remain alive in a suspended state.
When going through the list slowly, processes end normally.

See attached screenshots for Process Explorer output.