always same error in perl debug?

[sean darcy]

F9, perl-5.10.0-38.fc9.i386

running perl -d myscript.pl, single-stepping, I always get the same 
error, even for really simple statments:

..........
    DB<1> s
main::(set-firewall.pl:13):
13:	my $len_ip_address ;
Use of uninitialized value $tid in concatenation (.) or string at 
/usr/lib/perl5/5.10.0/perl5db.pl line 2227.
  at /usr/lib/perl5/5.10.0/perl5db.pl line 2227
	DB::DB called at set-firewall.pl line 13
   DB<1> s
main::(set-firewall.pl:14):
14:	my $real_ip_address;
Use of uninitialized value $tid in concatenation (.) or string at 
/usr/lib/perl5/5.10.0/perl5db.pl line 2227.
  at /usr/lib/perl5/5.10.0/perl5db.pl line 2227
	DB::DB called at set-firewall.pl line 14
.............

It looks to me like it's reporting an error with 
/usr/lib/perl5/5.10.0/perl5db.pl line 2227, not with my script.

So is this a perl bug? Or am I missing something?

sean