The pattern terminal behavior when you're making processing patterns is a bit different than it was in 1.7.10 in terms of clicking with the mouse. It's quite a bit different if you're used to the details of 1.7.10 but nothing gamebreaking.
This probably is more of a suggestion than a bug, as it's just behavior that's a bit different.
You can take a full stack of an item, and left click it in to specify that item, and that stacksize.
A right click with the item will tell it to take the item, but only specify 1.
You can increase or decrease the amount afterwards by right or left clicking on that item.
Left clicking with an empty hand clears it, right clicking decreases the amount by 1.
If you're holding the exact item and left click it'll increase the amount.
In this version if you either right or left click with any item it will take the item, AND the stacksize. Whether or not you left or right clicked. The amount will be the amount you had in your hand, no exceptions.
You are also not able to increase or decrease the stacksize afterwards.
Right or left clicking with an empty hand on the item will clear the spot in the recipe.
Fixes #2556, #2579: Restore old click behaviour.
Followup #2556, #2579: Prevent negative stacksizes.