Why does Ctrl-Z on Windows Git bash shell fail?

I sometimes have to work in Windows, which often means using the Bash shell. If I am (for example) in vim (not gvim) with several files open, and I hit CtrlZ to briefly go back to the shell and do something before returning to vim, instead of suspending my vim process Git Bash creates a new DOS shell. This is the last thing I'd ever want. Googling turns up nothing useful (at this point in time - YMMV in my future). What is going on?