What happened to the linear point curve in LRC??

In the midst of creating a develop preset today I hit a new roadblock: the curve panel is no longer a fully adjustable linear point curve. Somebody put training wheels on it. You can no longer grab the corner point of a curve and push it up or down!  It is now locked in place and only allows modest adjustment. This is a travesty!

There seems to be no button, menu or command to change the curve back into a fully adjustable linear point curve, the kind that skilled professionals need to use every day.

Today I was trying to create a develop preset to reverse a negative image into a positive. Before it was a piece of cake with the linear point curve. Now it appears to be impossible!

What gives? Somebody please point out what I am missing. Thanks in advance.