git commit <path> scanning entire working tree?

When I do a 'git commit <path to a single file>', git seems to scan
the entire working tree. Since my tree is relatively large (and when
on Windows, stat'ing is even slower), it takes quite a while (5 or so
seconds) before I can even edit the commit message.

Is there a reason it needs to scan like this when the commit command
specifies a specific path? It seems like it would only need to scan
the path I've specified.