Have you gone through Basic debugging checklist? Sounds like you've now done part (using the debugger), but maybe not everything: Does your $opts{defaults} really contain what you think it does when it enters the sub you showed? If not, then the problem lies outside of what you've shown. If it does contain what you think it should, then give us a security-redacted version of $opt{defaults}, because we cannot debug your logic in that sub without knowing what's there. See also SSCCE, How to ask better questions using Test::More and sample data, and How do I change/delete my post?

edit: add "everything": I had intended the "but maybe not: ..." to be one logical thought, separate from "you've now done part"... but when re-reading, it looked more like I was saying OP hadn't done even the running-the-debugger, which was not what I meant. sorry. /edit

Actually, I think I've identified the problem. It appears it is working as long as there are NO SPACES in the setting lines in the MySQL defaults file. If there are spaces around the "=", the setting is not read.

So a defaults file containing:

[mysql]
user=fred
host=mydb.localdomain
password=BANANA
[download]

works, but:

[mysql]
user = fred
host = mydb.localdomain
password = BANANA
[download]

does not.

What module did you use for reading/parsing your INI file? Config::Tiny? Config::Simple? Config::INI? Something else? Or did you roll your own?

For example, Config::Tiny handles spaces around the equals just fine:

#!/usr/bin/perl -l
use warnings;
use strict;

use Config::Tiny;
my $ini_string = <<"EOINI";
a=nospace
b = space
[GROUP1]
c=nospace
d = space
EOINI

my $cfg = Config::Tiny->read_string($ini_string);

use Data::Dumper; $Data::Dumper::Indent = 0;
print Dumper $cfg;
__END__
__OUTPUT__
$VAR1 = bless( {'_' => {'a' => 'nospace','b' => 'space'},'GROUP1' => {
+'d' => 'space','c' => 'nospace'}}, 'Config::Tiny' );
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I don't have the other two installed, but Config::INI claims to handle spaces around the equals, and Config::Simple's claim of "whitespace support" implies to me that it might

Seriously? Are you sure you had not changed anything other than spaces around "=" in the mysql defaults file?