Masking question

My workflow is to create a gamma curve with a linear gradient mask.  Then I make a new mask to adjust endpoints, again using a linear gradient.  With the second mask, the gaama curve persists in the tone curve window insstead of getting a new straigth line (linear curve).  If I then click on "linear curve", the changes mades with the gamma curve disappear.  I've played with checking and unchecking the "reset sliders aumatomatically" but it makes no difference.  Any suggestions as to what settings I need to change?