[2.4, UI] Dismissing an error on the UI, will make it never appear again

In the UI, I see an error such as the one in comment #1. Once I hit 'dismiss' and try to reproduce the error, I see no notification in the UI, however, I do see this in the logs:

Apr 24 19:43:14 localhost maas.bootsources: [error] Failed to import images from http://images.maas.io/ephemeral-v3/daily/: HTTPConnectionPool(host='10.90.90.1', port=8000): Max retries exceeded with url: http:/
/images.maas.io/ephemeral-v3/daily/streams/v1/index.sjson (Caused by ProxyError('Cannot connect to proxy.', NewConnectionError('<urllib3.connection.HTTPConnection object at 0x7f5ae4e867f0>: Failed to establish a
 new connection: [Errno 111] Connection refused',)))

How to reproduce:

1. Settings > Network Services > Proxy > External proxy and point MAAS to self caching proxy e.g. http://maas-ip:8000/
2. manually edit /var/lib/maas/maas-proxy.conf and remove the ACL on the same subnet as 1's maas-ip above.
3. Try to import images. You will see error above.
4. DIsmiss notification
5. Try to import images again.

WHat you will see is that the error is shown in the maas logs (maas.log) but not on the UI after the notification was dismissed.