I was in your same pitfall some years ago, then i learned to double check the the docs if something looks strange:

If LIMIT is omitted (or, equivalently, zero), then it is usually treat
+ed as if it were instead negative but with the exception that trailin
+g empty fields are stripped (empty leading fields are always preserve
+d);
[download]

The output you want can be obtained with a -1 LIMIT:

perl -MData::Dumper -e "$str='foo:bar:'; ($x,@opt)=split /:/,$str,-1;p
+rint Dumper ($x,\@opt)"
$VAR1 = 'foo';
$VAR2 = [
          'bar',
          ''
        ];
[download]

HtH
L*