It is a bug that has been acknowledged by Adobe. It happens on any text that has been scaled.
There is 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
Note : The workaround does not work backwards - you must enter in the properties box.
The workaround isn't working this morning on a file it worked on last night