Broken implicit withdrawal of route following interface down event

[agember]

I am observing strange behavior where GoBGP repeatedly withdraws a route and re-adds the same route with an additional community appended up until it eventually crashes. The behavior starts immediately after Zebra reports a status change in the interface over which the route advertisement was originally received, so I think the bug may be related to interactions with Zebra.

The attached configs and logs demonstrate the problem. Line 750 in Koper.gobgpd.log is where the update from Zebra is received and line 756 is where the first implicit withdrawal for a route for 128.0.2.0/24 occurs. The link that goes down connects Koper with its neighbor Ljubljana. Ljubljana.gobgpd.log shows the events that happened on Ljubljana. (Note that I am trying to ascertain how the network behaves when links fail, so there are many interface up/down events in the logs.) Koper.gobgp.txt and
Ljubljana.gobgp.txt are the configs for Koper and Ljubljana.

I can provide configs/logs from other devices in the network if they are useful.

[agember]

I observed this behavior with version GoBGP 1.33 (commit 8e6bd4c) as well as commit 71e56c5. I cannot easily test with the latest version of master using my setup due to issue #1831.