For example, see that this prints the same address twice.

No, it does not, at least not in perl v5.10.0:

perl -we 'sub f { my $t; sub { $t } }; $x = f(); $y = f(); warn "$x $y
+";'
CODE(0x82998c4) CODE(0x8299964) at -e line 1.
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Has perl become smarter?