As the poster mentioned in his update, Surefly Tech Supported confirmed the hypothetical would not happen after engine start. The poster who mentioned a backfire on start stated it was due to a weak battery.
Bottom line is that if you are going to have an electronic ignition, then you need a dependable electrical system. The ignition coil is magnetized by current flow. When you remove the current flow, this magnetic field collapses and a surge of current is able to jump the gap in the spark plug. A magneto does this with points that open the magnetic circuit, allowing the field to collapse, creating a spark. An electronic ignition does this with a solid state circuit board. If you remove power from that circuit board when the coil is charged, you may have enough energy to get a spark. This is common with all electronic ignitions.
A weak battery, bad starter, corroded electrical connections etc. will cause the starter to hang as the piston compresses the cylinder. The voltage will drop dramatically. If the voltage drops below the operating limit of the any EIS, it may spark. But, we are talking about just a few degrees BTDC, extremely slow rotation of the engine, hence the back spin of the engine.
I suspect the reason that SF told you itís a non-issue after start is because the system is designed to only charge the coil while the engine is in a safe zone for a spark? I would guess the FAA testing would have addressed this scenario.
No system is without compromise. Fortunately, you have a choice. A magneto that has a 500 inspection requirement due to multiple failures. Or an EIS that appears to have solid reliability in the field.