Like the other AM said, its a feature , but while delete will work, so will -override and creating a new cgi object

#!/usr/bin/perl --
use CGI;
use strict; use warnings;
my $q = CGI->new({1,-sham});
print join qq{\n},
        $q->textfield(-name,1,-value,2),
        $q->textfield(-name,1,-value,2, -override,1),
        CGI->new({})->textfield(-name,1,-value,2),
;;;;;;;
__END__
<input type="text" name="1" value="-sham" />
<input type="text" name="1" value="2" />
<input type="text" name="1" value="2" />
[download]

If you don't want any of the previous values, create new a object initialized from a hash  CGI->new({})

If you want to override some, don't delete them, -override => 1