I do not know what the exact trigger is.
Thinking similar.
My theory is when the combines come in cutting the corn, this major disturbance at least causes the deer to "head for the hills". Once there, they discover the acorns, which they then prefer over corn. But just like us humans, they prefer some diversity in the diets, and will still go back to those corn fields at night for "dessert".
I'm also of the opinion most hunters do not appreciate just how much linear distance deer habitually travel in a day. It's simply common for deer to travel over a linear mile every night from a heavy cover area to more open feeding areas. This travel distance gets expanded during the rut, and seems to be greatly contracted during the spring & summer months.
That said, I observed a bachelor group of bucks last year daily travel over a mile from their daytime to nighttime areas. What was most interesting, is they were using some different areas for nighttime feeding, sometimes traveling over a mile to the east, the next day over a mile to the west, the next day to the south (different fields, different directions).
The distance these deer were weekly using during the summer months was somewhat a revelation to me. Talking weekly maybe walking around on over 2,000 acres. Then in October, they scattered like a covey of quail.