Digital BW, The Print

I've effectively used this before to lower contrast, but it appears to 
no longer be working.  When I move either the highlight or shadow 
slider out of the 0% position, the entire image immediately jumps into 
very high contrast.  Anyone with any idea about this?  I've tested 
numerous images in both 8 and 16 bit and can no longer get it to work.  
I believe there is a variable here I am not accounting for.

I have never been able to replicate the function of this command with 
other tone controls, so I'd like to be able to use it.

Thanks,
Walt