Cannot use 0.125 as step size

[MarkJeronimus]

When you set step size to 0.125, the step size is remembered in full accuracy, but when you move keys on the keyboard, the coordinates are rounded to the nearest two decimal places.

Because of this, using the keyboard to move the keys left subtracts 0.12 but moving right adds 0.13. Repeatedly alternating between left and right causes the key to wander.

[ellisgl]

#273