Perhaps I should have said "If I write, is it possible I will succeed". My point is that the documentation (perldoc) clearly states " -w File is writable by effective uid/gid". It does not say "The write flag is set".
I appreciate I am going to get nowhere with this argument. It is just irksome to have to revisit a mountain of code to take this into consideration now that our automounted filesystems are more frequently unmounted.