I have my image mode set to CMYK. But as soon as I enter 0 C, 0 M, 0 Y, 50% K, it changes it 43% C, 35% M, 35% Y, 1% K. Attached is a screenshot.
How do I remedy this?
You have "Only Web Colors" selected. Turn that off as its essentially irrelevant on modern computers. It's trying to figure out how to best represent 50% K in a vastly reduced RGB palette known as Web Safe Colors.