Why can't I add a constant power fade to these clips?

Hey guys, 

I've been having this problem since there was an Adobe update a few months ago. I'm pretty sure it has something to do with my "handles"? Why can't I add a constant power to these audio tracks? What do I need to do to ensure I can always add a constant power and that it will be able to centre between the two tracks? 

See screenshot attached. 

Thanks in advance, 

Fin