Capital city disappears when a city state captures it

[TomKQT]

I was keeping the health of Sparta (no wall) at zero with my Saka Horse Archers while waiting for a melee unit to come and capture the city and I didn't pay much attention to a city state warrior standing next to the city. While suddenly the warrior captured the city and weird things started to happen. Gorgo showed up with her last words about being defeated, but only half of it was spoken (the voice stopped). The confirmation button was there, but had to be pressed twice and led to some weird screen with details about a leader (other than her). When I closed this screen I noticed that the city was completely removed from the world...
I reloaded and tried it again and everything happened exactly the same way. When I reloaded an even older save and blocked the warrior, I managed to capture the city myself and everything worked properly (including the voice of Gorgo).

Anyone else noticed this? I think it's quire rare to see a city state capure a city - and this was even the capital. This could easily be overlooked by beta testers.

Version: 1.0.0.26 (221715)