Getting 0.8 mm wall thickness instead of 0.4mm

[anothervoron 0]

I'm trying to print a hollow cube to calibrate the flow. I tried two wall lines but it gave me 1.2 mm (sounds like 3x0.4mm). I reduced the line count to 1 and now I get 0.8mm wide wall. I do not see a second line (the printer does not passes two times over the same layer). It seems like the width of the line is 0.8 mm which is super strange.

 

Here are my settings:

 

I have a 0.4 mm nozzle.

Edited May 23, 2021 by anothervoron