That's your problem: my makes a variable lexical, and symbolic references only work with dynamic/global variables. BTW, this is also why mixing eval STRING with lexicals is problematic:

foobar:perl/blead% perl -le '$y="print \$x"; $z=sub { my $x=23; $y}; e
+val $z->()'

foobar:perl/blead% perl -le '$y="print \$x"; $z=sub { $x=23; $y}; eval
+ $z->()'
23
[download]