>c:\progs\perl588\bin\perl 722505.pl
pre
STORE undef
post
STORE undef

pre
STORE undef
STORE [a]
post
STORE undef

>c:\progs\perl589\bin\perl 722505.pl
pre
STORE undef
post
STORE undef

pre
STORE undef        <-- Still there
STORE [a]
post
STORE undef