bird >=2.0.4 Stack underflow and most routes become filtered

[Дружок 1]

Hi!
..
/var/log/bird.log
2019-08-22 15:38:38.604 <ERR> filters, line 1023: Stack underflow
2019-08-22 18:02:27.157 <ERR> filters, line 511: Stack underflow
2019-08-22 18:02:30.616 <ERR> filters, line 0: Stack underflow....
...
function bgp_in(int peer_as; prefix set peer_nets)
{
        if ! (avoid_martians()) then return false;
        if ! (net ~ peer_nets) then return false;
        if (bgp_path.first != peer_as ) then return false;
   #   if (is_black()) then return true;
   #   if net.len > 24 then return false;
        return true;
}
..
define DataClub_nets = [
    46.183.216.0/21{21,32} <http://46.183.216.0/21%7B21,32%7D>,
    84.38.128.0/24{24,32} <http://84.38.128.0/24%7B24,32%7D>,
    84.38.130.0/24{24,32} <http://84.38.130.0/24%7B24,32%7D>,
    84.38.131.0/24{24,32} <http://84.38.131.0/24%7B24,32%7D>,
    84.38.132.0/24{24,32} <http://84.38.132.0/24%7B24,32%7D>,
    84.38.134.0/24{24,32} <http://84.38.134.0/24%7B24,32%7D>,
    84.38.135.0/24{24,32} <http://84.38.135.0/24%7B24,32%7D>,
    109.248.147.0/24{24,32} <http://109.248.147.0/24%7B24,32%7D>,
    109.248.148.0/24{24,32} <http://109.248.148.0/24%7B24,32%7D>,
    109.248.149.0/24{24,32} <http://109.248.149.0/24%7B24,32%7D>,
    185.220.116.0/24{24,32} <http://185.220.116.0/24%7B24,32%7D>,
    185.220.117.0/24{24,32} <http://185.220.117.0/24%7B24,32%7D>,
    185.220.118.0/24{24,32} <http://185.220.118.0/24%7B24,32%7D>,
    194.165.16.0/23{23,32} <http://194.165.16.0/23%7B23,32%7D>
];
..
protocol bgp DataClub from PEERS {
        description "DataClub/52048/as-dataclub";
        neighbor 193.27.39.4 as 52048;
        ipv4 {
                import where bgp_in(52048, DataClub_nets);
                export where bgp_out(52048, 64004);
        };
}
...

I redid the configuration something like
...
ipv4 { import filter myfilter; ..
...
then I issue test "show route filter myfilter" and get all nets. But in
fact, all these routes were filtered.
And, finally, only "accept" remained in the filter - this method unfiltered
routes.
Bug, feature?
P.S.:  Bird <= 2.0.3 is OK.
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