"Two live, catchable Pokémon spawning on top of each other"

#PokemonGO: It is my understanding from previous research that all Pokémon spawn inside/at the center of a level 20 S2 cell. When two Pokémon spawn on top of each other, then that means that one of them have despawned - one of them will be catchable and the other will result in an error and will immediately disappear when tapping it on the map.Recently I found a location that defies this rule. The spot seems to spawn two Pokémon on top of each other, but both are catchable. Can someone shed some light on what is going on? I thought that it would be impossible for this to happen.ScreenshotAnother angle - the left Pokémon (Pikachu and Staryu) has one catchable spawn and one timed out spawn; the right two (Pikachu and Chinchou) however are both catchableCircles closeup - this is from another spawn instance but the same location - you can see that there is a very, very slight difference in the circle locations, but there is no way two S2 level 20 cell centers can be that close togetherVideo proof that both are catchable (i.e. not a timed out spawn)The location is 27.7714, -15.69584; tried putting this into an S2 coverer but couldn't conclusively determine the exact cell boundaries on the screenshot.I have no idea what is going on here. As it can be hard to keep up with everything on TSR - is it common knowledge that this can happen? I've never seen this happen before. via /r/TheSilphRoad http://bit.ly/2VgFWeE