Solved [BUG] Mill produces a max of two stacks of output for any one given input.

[Satozaki]

The Mill has a hard cap of outputting two stacks for an input, if I put in a full 999 stack of Beet, the next day there are only two stacks of Sugar (should be three).
The reason for the bug is a slight error in Utility.addItemToThisInventoryList(Item, IList<Item>, int), in the end code block:

if (i.Stack > i.maximumStackSize())
{
Item tmp = i.getOne();
tmp.Stack = i.maximumStackSize();
i.Stack -= i.maximumStackSize();
list.Add(tmp);
continue;
}

The line:
i.Stack -= i.maximumStackSize();

should actually be
(i as StardewValley.Object).stack.Value -= i.maximumStackSize();

This is because the Object.Stack accessors clamps the value to maximumStackSize() effectively just setting the new Stack value to the maxStackSize, instead of just removing the maxStackSize

 

[Odin]

This should be fixed in 1.5.2! Please mention if it's still an issue for you!