If I select G-Code Flavor: Mach3/LinuxCNC, I get no spiral part of the gcode. It works if I select Marlin (although this Gcode isn't usable on a linuxcnc machine). I tried this on 1.20 and 1.21.
This example gcode shows the transition from bottom layers to spiral. The x/y barely move, and Z keeps increasing...
G1 X3.577 Y13.021 A41.70256
G1 X1.794 Y13.285 A41.80276
G1 X0.673 Y13.340 A41.86511
G0 Z0.700 F13200.000
G0 X0.659 Y13.047 F13200.000
G0 Z1.000 F13200.000
G0 X0.646 Y12.796 F13200.000
G0 Z1.300 F13200.000
G0 X0.634 Y12.544 F13200.000
G0 Z1.600 F13200.000
G0 X0.622 Y12.293 F13200.000
G0 Z1.900 F13200.000
G0 X0.610 Y12.042 F13200.000
G0 Z2.200 F13200.000
Right. That's because Spiral vase acts as a G-code filter and it looks for E instead of A.
One other issue with spiral vase - you need to have Print Settings | Layers and Perimeters | Advanced | Seam Position - set to Algined. Random breaks spiral vase.
Bugfix: spiral vase was not working when extrusion axis was not E. #2350
I fixed the mach3 issue. Thank you for reporting that.
Regarding your last comment, the Seam Position option is ignored when using Spiral Vase. Can you check with Slic3r 1.2.1?
It looks ok. I was running from source (master) with a version between 1.2.0 and 1.2.1. I had some other strange behaviours (missing layers when scaling) but that has all gone away with what is currently in master (so I can use the mach3/linuxcnc spiral vase).
PS mach3/linuxcnc do use G0