ah, interesting!

$ perl -le'@@=qw( a b ); print qr|\Q@@|'
(?-xism:\@\@)

$ perl -le'@@=qw( a b ); print qr|@@|'
(?-xism:@@)

$ perl -le'@a=qw( a b ); print qr|\Q@a|'
(?-xism:a\ b)
[download]

I knew something was hinky with what I had posted.