Ever since the latest update of Photoshop I cant use the Leading tool in Photoshop. If I use my keyboard keys to try and open or close the space it always makes the space bigger. Also if I try and type a specific number in it seems to just randomly put in a huge number sometimes up to 4000.
It is a bug that came in with CC2018 and it affects text that has been transformed. Adobe are working on a fix.
In the meantime 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.
But just an FYI its happening for me without text transform. I just type, select my font and it goes crazy when I try to adjust line spacing. I have not scaled any of the text at all.