This software bug needs to be finally stopped after 25 years:
The default settings provided caused the roundness not working for me, late last year it worked the first time in my life,
after I edited the default "0 mil" text. I didn't suspect that the DRC window would ignore all human logic.
Also, the old manual did not suggest that all those "0 mil" values absolutely must be changed for Eagle to work properly.
Bugs: 1) the DRC settings window did not make a value correction, 2) the actual code responsible for the function did not make the check and correction.
(if you look at a mechanical range, where maximum is 0/0.0254 mm and minimum is above that, and you trace a line from maximum to lower values, you will go lower and lower, until you reach the minimum, you will arrive at negative infinity before reaching the minimum.)
If such primitive elementary check logic is not present here, we can reasonably assume it is nowhere to be seen in the rest of the huge code base, causing all kinds of bugs. I have multiple redundant safety checks in all my code. It always works as expected when it runs.