Carsten,

Did you perform your test with the engine on a test stand or in an airplane?

It would be very educational to look at the voltage of the rx with servos idle, servos all moving as in during a snap and the voltage taken when the servos have vibration applied to them as they are during normal flight. (with and without ignition)

This information would very helpful, that being said, hundreds of flights have been flown with the CDI pluged directly into a Futaba Fasst RX 6014, never a hold or glitch, three different airframes and three different igntion modules.

No doubt that the safest would be a separate battery and switch.

Bill