it is fairly clear that this particular subtlety of Perl (and Perl has a lot of them) had escaped OP

Indeed, that's true. I included the parenthetical remark to head off any suggestions that the problem was caused by precedence. Since I had ruled that out, I obviously didn't think that was the problem, but I didn't investigate enough to find out what it was. I just assumed it was something Perl wouldn't allow. Your quoted snippet cleared up the exact reason, and I appreciate it.