I have the BME and had the standard ignition set-up (rubber boot, ground braid secured to the spark plug base with a hose clamp) and developed ignition interference after about 15 flights. I found no obvious cause other that gunk accumulated on the spark plug threads, perhaps interfering with grounding. I switched to the Bosch cap with a new plug and store the plane with the engine upright and the problem has not recurred so far.

Peter