Explain a difference between filters??

[Владислав Гришин]

Part of bird.conf

...

filter export_default_1 {
        if net ~ [ 0.0.0.0/0 ] then accept;
        reject;
    }

filter export_default_2 {
        if net ~ 0.0.0.0/0 then accept;
        reject;
    }

filter export_net_1 {
        if net ~ [ 12.12.12.12/30 ] then accept;
        reject;
    }

filter export_net_2 {
        if net ~ 12.12.12.12/30 then accept;
        reject;
    }

bird> show route filter export_net_1
12.12.12.12/30     via 10.10.1.3 on eth1.550 [myospf 2010-05-08 18:54:23] *
E2 (150/10/20) [10.10.1.3]

bird> show route filter export_net_2
12.12.12.12/30     via 10.10.1.3 on eth1.550 [myospf 2010-05-08 18:54:23] *
E2 (150/10/20) [10.10.1.3]

bird> show route filter export_default_1
0.0.0.0/0          via 93.191.9.205 on eth2.701 [static1 2010-05-09
16:31:10] * (254)
                   via 93.191.9.205 on eth2.701 [bgpfiord 2010-05-08
18:54:21] (100) [AS28917i]
                   via 82.138.44.129 on eth2.51 [bgpcomcor 2010-05-08
18:54:15] (100) [AS8732i]

bird> show route filter export_default_2
0.0.0.0/0          via 93.191.9.205 on eth2.701 [static1 2010-05-09
16:31:10] * (254)
                   via 93.191.9.205 on eth2.701 [bgpfiord 2010-05-08
18:54:21] (100) [AS28917i]
                   via 82.138.44.129 on eth2.51 [bgpcomcor 2010-05-08
18:54:15] (100) [AS8732i]
12.12.12.12/30     via 10.10.1.3 on eth1.550 [myospf 2010-05-08 18:54:23] *
E2 (150/10/20) [10.10.1.3]
208.0.208.0/22     via 93.191.9.205 on eth2.701 [bgpfiord 2010-05-08
18:54:41] * (100) [AS26759i]
                   via 82.138.44.129 on eth2.51 [bgpcomcor 2010-05-08
18:54:24] (100) [AS26759i]
40.0.40.0/24       via 93.191.9.205 on eth2.701 [bgpfiord 2010-05-08
18:55:07] * (100) [AS4249i]
                   via 82.138.44.129 on eth2.51 [bgpcomcor 2010-05-08
18:54:49] (100) [AS4249i]
69.0.69.0/24       via 93.191.9.205 on eth2.701 [bgpfiord 2010-05-08
18:55:20] * (100) [AS19374i]
                   via 82.138.44.129 on eth2.51 [bgpcomcor 2010-05-08
18:54:48] (100) [AS19374i]
...  more output 
8.2.0.0/24         via 93.191.9.205 on eth2.701 [bgpfiord 2010-05-08
18:55:10] * (100) [AS20473i]
                   via 82.138.44.129 on eth2.51 [bgpcomcor 2010-05-08
18:54:25] (100) [AS20473i]
200.2.192.0/19     via 93.191.9.205 on eth2.701 [bgpfiord 2010-05-08
18:55:22] * (100) [AS10778i]
                   via 82.138.44.129 on eth2.51 [bgpcomcor 2010-05-08
18:54:26] (100) [AS10778i]
72.2.64.0/19       via 93.191.9.205 on eth2.701 [bgpfiord 2010-05-08
18:55:08] * (100) [AS19009i]
                   via 82.138.44.129 on eth2.51 [bgpcomcor 2010-05-08
18:54:28] (100) [AS19009i]
69.2.77.0/24       via 93.191.9.205 on eth2.701 [bgpfiord 2010-05-08
18:54:52] * (100) [AS15105i]
                   via 82.138.44.129 on eth2.51 [bgpcomcor 2010-05-08
18:55:07] (100) [AS15105i]
--More--
...  more output

Why filters export_net_1 and export_net_2 work equally, and/but filters
export_default_1 and export_default_1 on a miscellaneous?
Why the filter export_default_2 "does not work" also as the filter
export_net_2 works?

Vladislav Grishin