This is a real pain, I've been fighting this all day in order to do some extrusion calibration. The slicer flat out won't even in vase mode and introduces artifacts that simply shouldn't be there. If it does it here it will do it elsewhere. This behaviour occurs regardless of the extra walls setting, vase mode, print thin walls etc etc.
The image below shows the corners as per Cura, this is a 0.42mm wall with a 0.42mm extrusion width, drawn in Fusion360. I've tried various widths from 0.40 and Cura simply cannot handle it, all corners appear as per the first image below.
There is no join anywhere but Cura is introducing one for every single corner even in vase mode, notice the second image that shows the bottom 3 layers forming the base have no such defect despite the single wall thickness. In my opinion this is a code defect that really needs to be addressed. The only way I can do this is to use Simplify3D which is an application I am trying to get away from, Prusaslicer doesn't generate reprap gcode well and I need to manually edit every gcode file it produces for my coreXY (Duet3).
I'm trying to establish a workflow where I need only one slicer, Prusa have dropped the ball by messing with filament availability in custom printers (even though I own a Prusa MK3S and buy Prusa filament), there slicer, their rules I suppose.