You said you; "thought it was a thing of the past", indicating that it is (still?) a problem?

It happened to the OP.

I think the problem--when it existed--was more a problem with the way perl assocs were set up (by AS)--not a fundamental issue with Windows redirection.

Lots of people are/were missing the %1 in their association. That's a different problem. It works fine for the OP when he provides an argument. It's when he redirects STDIN that he has a problem.