While I was trying to learn something about perl internals and playing with Devel::Peek, I noticed the following behavior that I don't understand. The following simple script: 
# devel.pl
use Devel::Peek;
my $a = undef;
Dump $a;
my $b = \$a; 
Dump $a; # note the reference count for $a

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produces the correct reference count for $a when running "perl -d devel.pl", the output is as follows: 
c:>perl -d devel.pl

Loading DB routines from perl5db.pl version 1.23
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(devel.pl:3):     my $a = undef;
  DB<1> n
main::(devel.pl:4):     Dump $a;
  DB<1> n
SV = NULL(0x0) at 0x1829ce0
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY)
main::(devel.pl:5):     my $b = \$a;
  DB<1> n
main::(devel.pl:6):     Dump $a;
  DB<1> n
SV = NULL(0x0) at 0x1829ce0
  REFCNT = 2             ###<----- correct count
  FLAGS = (PADBUSY,PADMY)

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But if I do an interactive session using "perl -de 1", it produces the wrong count for $a: 
c:>perl -de 1

Loading DB routines from perl5db.pl version 1.23
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(-e:1):   1
  DB<1> use Devel::Peek;

  DB<2> my $a = undef;

  DB<3> Dump $a;
SV = NULL(0x0) at 0x1aeccfc
  REFCNT = 1
  FLAGS = ()

  DB<4> my $b = \$a;

  DB<5> Dump $a;
SV = NULL(0x0) at 0x1aeccfc
  REFCNT = 1       ###<----- wrong reference count
  FLAGS = ()

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However, if I do not use "my" in the above interactive session, all is well: 
c:>perl -de 1

Loading DB routines from perl5db.pl version 1.23
Editor support available.

Enter h or `h h' for help, or `perldoc perldebug' for more help.

main::(-e:1):   1
  DB<1> use Devel::Peek;

  DB<2> $a = undef;

  DB<3> Dump $a;
SV = NULL(0x0) at 0x1aecc18
  REFCNT = 1
  FLAGS = ()

  DB<4> $b = \$a;

  DB<5> Dump $a;
SV = NULL(0x0) at 0x1aecc18
  REFCNT = 2        ###<--------correct here
  FLAGS = ()

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What's going on here?

In reply to Strange behavior of "my" in "perl -d" and "perl -de" by johnnywang

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