I clicked on the rattata on the map and it did the small intro animation after that the background on the catch screen, I don't use AR, turned black from the bottom to the top. The rattata was still visible and jumped up and down and thw circle also still worked. However all other icons including the Pokeball vanised.
I didn't manage to reproduce this, so I don't know what caused it. The only way to fix it was to restart the app. Has anyone encountered something similar, or knows the cause?