The entries were probably not dropped, but overwritten:
$hash{entry} = "will get lost";
$hash{entry} = "this will replace it";
print $hash{entry};

[download]
In order to catch the error, you need to change the code that loads the values. Instead of $hash{$key} = $value you might use 
die "Error: duplicate value for $key\n" if exists $hash{$key};
$hash{$key} = $value;

[download]
See also perldata, or even perldsc on how to store several values at the same key.

In reply to Re: eval question by choroba
in thread eval question by jhuijsing

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