I have a Mercurial repository which has many Git subrepositories in it. When I open TortoiseHg Workbench and run any commands (even just click the top "Working Directory" row), a number of git.exe command windows appear and disappear quickly. Since it is hard to explain only with a text, I record a video and here is a link.
My environments are as follows. Windows 7 Professional 64bit TortoiseHg 2.1.4