It sounds like you are having the same issue reported in several threads with entering the leading value. It happens on text that has been transformed.
Adobe have acknowledged a bug but in the meantime you can use a workaround:
a. Enter the leading value in the Properties panel.
b. When you hit enter the value in the properties panel box will change to something different (that is a bug) but will now show correctly in the Character panel
c. The value applied to the text will be the same as you entered and now shown in the character panel
So you end up with different values shown in the two panels but the value entered in properties and now shown in character will be applied.
Note : The workaround does not work backwards - you must enter in the properties box.
Thank you. Inputting the value worked in the properties panel.