In the Symbology - Graduated Colors - Method (Manual Interval), I cannot modify the existing Upper Value to anything but a whole number. In the screen shot below, I started with another method by default and changed the Method to Manual Interval. Both values had decimals in them. When I tried to change those values, it would not let me add a decimal. In fact, when I deleted the tens decimal place, the decimal disappeared along with the tens position number without another backspace press.
Is there a setting that I have to find and change? If not, this should be a bug entry.