docker containers connected to a network when run won't show up in network_object.containers field

when running a container with

client.containers.run(.....,
                                 network=net1,
                                 ......)

the container ends up connected to the network, but when calling net1.containers on the network object, it returns an empty list ([])
When re-getting the network object with
client.networks.get(net1_name),
the container shows up.

to reproduce this bug:

1. create a network object with client.networks.create
2. run a container with client.containers.run, with parameter network = (the name of the net you created)
3. check network_object.containers field and see it's empty
4. do client.networks.get(net1_name) to re-get the object and see that now the container is present in
   checked this issue with two different hosts with different docker versions, both reproduced the bug.

Reproduce the sequence using client.networks.create, client.containers.run with the network name, and client.networks.get, then inspect how network_object.containers is populated and refreshed. No file or test is named in the issue; done means the original network object reports the connected container without requiring a second get.