Isn't this just an ordering issue ?
The compiler hasn't seen the definition for sub_c when it compiles sub_b, but it has by the time it gets to the stand alone call of sub_c, hence the differing behaviour. So if you swap the order of your functions it will do what you want.
use strict;
use Data::Dumper;
sub sub_c (\%)
{
my ($hash1c) = @_;
print "sub_c arguments:" . Dumper (@_);
}
sub sub_b ()
{
my %hash1b = ();
$hash1b{"key1"} = "1";
print "calling sub_c from sub_b\n";
sub_c (%hash1b);
}
my %hash1a = ();
$hash1a{"key1"} = "1";
print "calling sub_b\n";
sub_b ();
print "\n";
print "calling sub_c directly\n";
sub_c (%hash1a);