Filter route attribute "from"

[Alex Rydzewski]

Good times, bird community!

I'm have trouble with filter routes by "from" attribute.

Routes in Bird route table have data about router which the route has 
originated from:
80.239.201.11/32   via 193.124.176.1 on eth1 [kernel1 2020-08-11] * (10)
10.0.0.0/30        via 10.0.0.18 on bond0 [MyOSPF 2020-11-09] * I 
(150/20) [172.21.1.1]
154.47.36.2/32     via 193.124.176.1 on eth1 [kernel1 2020-08-13] * (10)

but if i try get that routes:
show route where from = 172.21.1.1

I get empty respond without any errors.

When I was add print statement to config for check which "from" 
attribute supplied to filter:
export filter { print "route: ", net, ", ", from, ", ", proto,; accept; };

I was saw that from is 0.0.0.0:
... bird: route: 172.21.24.0/23, 0.0.0.0, MyOSPF

The issue is observed with 1.4 and 1.6 bird versions.

Explain me please, what i understand wrong about that?