The immediate source of your problem is that SQL::Parser (the parser used by SQL::Statement) has the following subroutine:

sub LIMIT_CLAUSE {
    my($self,$limit_clause) = @_;
#    $limit_clause = trim($limit_clause);
    $limit_clause =~ s/^\s+//;
    $limit_clause =~ s/\s+$//;

    return 1 if !$limit_clause;
    my($offset,$limit,$junk) = split /,/, $limit_clause;
    return $self->do_err('Bad limit clause!')
         if (defined $limit and $limit =~ /[^\d]/)
         or ( defined $offset and $offset =~ /[^\d]/ )
         or defined $junk;
    if (defined $offset and !defined $limit) {
        $limit = $offset;
        undef $offset;
    }
    $self->{"struct"}->{"limit_clause"} = {
        limit  => $limit,
        offset => $offset,
     };
     return 1;
}
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The important part is the middle. SQL::Parser demands that all parameters to a LIMIT clause be numeric. This is inline with most (but not all) DBD::'s. The major exception is DBD::mysql, which allows parameters in LIMIT clauses (with certain restrictions).

If you feel that this is a useful feature, provide a few test cases for the author. Better is the patch as well, but the test cases are a minimum.