I've never ran into this issue before. I select a line and I want to extent it by "x" amount of units by simply clicking on the blue boxed endpoints. In the past it has always showed up as an extention and displays how many units I am extending it, however instead my polar tracking is showing up and gives me the entire length of the line. So whatever input I put in will not add or subtract to the length but change the length to whatever input I put in. Is there a way I can have the extension show up without continuously turning polar tracking on and off?
Check the system variable POLARMODE. Mine is set to 2 and works the way you desire.