Can a PPM transmitter on the same channel as a PCM transmitter cause the PCM plane to crash? PCM is NOT in failsafe mode.

We have conducted some tests which showed PPM did not affect PCM, but last week a PCM system took off on my channel (I was posted and legal). My PPM plane being preflighted in the pits was acting strange. I finally pulled out my antenna full length and at that time the PCM plane over the end of the runway fatally crashed. No controversy over whose fault, he admitted it. If I had taken off first, he would have shot me down and owed me a plane.

We have a confirmed PCM flyer who claims when on PCM, a PPM signal will not cause him to crash. The above episode tends to prove him false. Who is correct?

Coop