windows grep messed up

[Larz60+]

I have long used windows (GNU) grep without incident ... until about 6 months ago
now when I use a command like:

grep -ri --include='*.py' 'messagebox' .

I immediately get an idle window with a copy of grep.py in it

Any clues on how to stop this most annoying behavior?

Same in cmder or cmd

I added an environment variable to no avail