I am not sure if you are disputing that such things exist, or making a sarcastic comment, but I know of at least one location where they literally put in a round about, that originally had normal roundabout entrances, but then someone complained a dug up some rule that said that anywhere a county and a city road met, there needed to be a 4 way stop. Now obviously this rule was intended to just make sure that such intersections were controlled, and was probably written before the US had really thought about round abouts as an option and a roundabout met the spirit of the rule just fine, but nevertheless it was a rule, and so they added a stop sign at each entrance.
So, if you were making a sarcastic joke: then yup, they managed to convert a round about into a 4-way stop with a (giant, view obstructing) island. But if you were arguing that no one would do such a thing as put stop signs at the entrances to a round about, I regret to inform you that they absolutely would.
Also, I'm now curious about the existence of "4-way stop with an island". Why would someone build that? It seems strictly worse than a regular 4 way stop.
Too many people remain at the stop sign until the roundabout completely clears, so it becomes an excruciatingly slow 4-way stop. And there's not much traffic there.
A few miles from that one, there's a high traffic roundabout that works very well. The heavily used right turn lanes are divided and don't enter the roundabout. There are very clear markings on the ground. And there are yield signs at the entrances, so people know what to do. Traffic flows great through it, with the heaviest direction of travel naturally getting more throughput.
They don't have to understand roundabouts specifically, there is supposed to be a yield sign when entering a roundabout - do they not understand the yield sign?
Or two near me have traffic lights very near (1/4 block or so) from the exit, meaning that traffic will inevitably back up into the roundabout, locking it up.