Cura Insisting on Two Inner Walls?

[carvedblock 3]

Hi, 

Please help me understand. 

I make a model with a shell exactly 1.2mm thick. 

 

I use .4mm nozzle with .4mm wall. 

 

Yet, Cura tries to fit in two inner walls, or at least moves twice in the inner space (not marked as travel move). 

Even though: 
- combing is off

- and I even turned on outer wall before inner with  minimum wall flow it 100%

- compensate wall overlap is off

What gives? Thanks!

This produced ugly blobs on my print and I really can't get rid of them (This is an edge case. I normally have no issue with blobs, even though I use a long and hot meltzone with stringy PETG for part strength.)

I am attaching the cura project and gcode and the stl so anyone can play. 
 

3walls.3mf 3walls.gcode

shell1.2mm.stl

Edited June 28, 2019 by carvedblock
Attach the stl for anyone to test.

[carvedblock 3]

Any ideas from anyone are highly appreciated. 

I hoped maybe you could chime in @smartavionics if you have a minute? I think you're the de-facto resident forum experts on shells, wall overlaps, and such things.

PS: S3D and Slic3r dont't do this and print the model just fine. 

[burtoogle 508]

Turn on the wall overlap compensation and set the min wall flow to, say, 40 (not really very critical). Hope this helps.