SourceTree ignores umask, changes all touched files' permissions to 644

SourceTree ignores the umask setting whenever it touches files in a git repo, which is counter to the way the actual git tool works. When cli git checks out a new file, or a checkout changes an existing file, those files' permissions are set according to the current umask value. But when SourceTree alters a file, the permissions are always set to 644, no matter what the umask value is. And yes, I've set the umask value for user applications, as specified in these instructions from Apple. This has no effect.

This is extremely disruptive to a project being worked on by multiple users on the same machine. My system's umask is 002, because I want group write permission on all my files. But every time anyone uses SourceTree, that group write flag is removed from the files in our repo.