perl -d: puzzling behavior when run in program in current directory

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$ cat abc.pl
print "hello world\n";
print "goodbye world\n";

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$ cd
$ perl ~/learn/perl/p5p/abc.pl
hello world
goodbye world

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$ perl -d ~/learn/perl/p5p/abc.pl

...
use o inhibit_exit to avoid stopping after program termination,
h q, h R or h o to get additional info.
  DB<1> q

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$ cd learn/perl/p5p
$ perl -d abc.pl
hello world
goodbye world
Var=

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$ cd xyz
$ perl -d ../abc.pl
...
use o inhibit_exit to avoid stopping after program termination,
h q, h R or h o to get additional info.
  DB<1> q

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$ echo $PERLDB_OPTS

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