Sounds like your coilpack may have an inbuilt igniter.
Spark inverted is dead simple. If you invert something you turn it upside down. With regards to Ms the processor its pin puts out two states +5v and 0v.
If you look at how ignition works you, 1. spend some time with the coil doing nothing then you, 2. switch the coil circuit on to charge it and 3. off again to discharge it and fire the plugs. The time from 2 to 3 is the magical dwell period people have trouble with. To achieve this switching sequence depends on the hardware in the ignition system. From the processors point you may need to go 0v for off then 5v for on then 0v for off for the cycle OR it may need to be inverted and go 5V for off then 0V for on then 5v for off. It will be hardware dependant.
Each driver could be another inversion of this signal. So with spark inverted you get correct function of the VB921 driver in the MS but if your coilpack has another driver inbuilt then the signal gets inverted again. To cure this you are having to not invert the source signal.