Unless I'm reading this wrong (certainly possible in my case), there really is a bug in S3D.
The bug is in the G-Code panel.
The checkbox we are turning off should have nothing to do with changing the extrusion mode from relative to absolute.
It should only change if G92 E0 commands are used during the print. (And as shown before both Kisslicer and Slic3r use those with no problem.
However, the checkbox above that IS the one that should control absolute mode (and the default as shown IS set for absolute, but it apparently isn't working correctly. (or probably more correctly, the G92 E0 checkbox is putting the g-code back to relative mode in error.)
The default options as shown should
produce g-code just like Kisslicer (absolute extrusion mode & resetting the extruder position as it goes through the file). But of course we now know it doesn't.
I looked at all the combinations of those two checkboxes and I didn't find any combination that created code in the same way as Kisslicer and Slic3r (although like I said, the combination shown above should do that).
So for now, just turning off the G92 E0 checkbox is the fix.
Also, checking both of those boxes seem to be a very weird (well at least to me) mode where there is both negative and positive retractions:
G1 X25.651 Y19.73 E0.1992
G1 E-0.5 F1800 <------
G0 X23.08 Y18.397 F4800
G1 E0.5 F1800 <------
G1 X23.76 Y18.14 E0.0242 F2880
I may try that but I've already wasted a lot of plastic on this thing