This happened twice in a row on one night in Realms.
The center of a fenced in potato crop was well lit on the sides but a little dark in the center at night. All the soil was tilled and every potato was fully grown, yet despite this a creeper spawned in the center of the farmland. A friend and I slayed it, but shortly after, I saw another creeper quite literally appear at the center of the crop again.
To stop the spawning, I lit up the center of the crop, but I found it strange the creepers spawned where they did because my friend told me after the first creeper appeared that mobs are not supposed to spawn on tilled ground and later I read elsewhere online the same thing.
I did check to see if there was an untilled spot of land among the potatoes after the two creepers were slayed but there was none.
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I did not expect it but from what I understood, after it happening twice at night the center of the potato crop will have to be just dark enough for a hostile mob to spawn on normal blocks. I, oblivious to the fact that mobs cannot spawn on tilled land, assumed a mob would spawn there at the center of the crop but my partner told me it was not possible. When it actually happened twice I found it hilarious and definitely off. I'll show a picture of the crop and how it was lit before we fixed it.
I did not expect it but from what I understood, after it happening twice at night the center of the potato crop will have to be just dark enough for a hostile mob to spawn on normal blocks. I, oblivious to the fact that mobs cannot spawn on tilled land, assumed a mob would spawn there at the center of the crop but my partner told me it was not possible. When it actually happened twice I found it hilarious and definitely off. I'll show a picture of the crop and how it was lit before we fixed it.
What it looked like up close and afar when it happened (after the event since I had not thought to bug report it until a day later). There is also show of the dimensions of the potato crop if that helps, though the crop was lit up properly in that picture. Neither my partner nor I expected the spawn and afterwards I did check for untilled soil but there was none. There were also no spiders in the crop and no jungle trees at the time of the creepers popping in. That side of the farm used to be unlit also.