Quantity selection menu's arrow-key inputs don't seem to work

[Former user]

When deciding how much of a liquid to pour or how many of an item to drop I get a quantity selection menu as shown in the attached png, instructing arrow key use. For me, the arrow keys don't work properly to adjust the quantity. I can use num2, num8, num4, and num6 instead, or hit backspace then type a number, but the arrow keys seem bugged.

Not using any mods, though I am using an ergodox keyboard, so if this isn't happening to most people, that seems like a possible explanation.