Problem with keyboard shortcut for font size in CC photoshop. The incriments sometimes work, i.e it goes 1 points at the time, but sometimes it goes 10 or even 20 points at the time. It seems to be very random. Any thoughts?

Problem with keyboard shortcut for font size in CC photoshop. The incriments sometimes work, i.e it goes 1 points at the time, but sometimes it goes 10 or even 20 points at the time. It seems to be very random. Any thoughts?