We use a rubric that has a range for each criterion as well. I just went into Speedgrader to look myself. When I select a range, it still allows me to edit the number. When I save what I have entered, the values shown reflect what I typed in, not the default value. It also seems to work regardless of whether I am using Classic or Enhanced Rubrics.
Are you in Speedgrader when doing this? Is it giving you any kind of message when you try to change the score?
Are you able to record your screen (hiding the student info) of you selecting a range but being unable to click on and change the value under points?
I'm curious if this is just something you are experiencing or if I can recreate the issue on my end.