When you shut the ignition off and the blower is still spinning, the blower then acts like a generator. So your getting voltage feed back to the ignition, to keep the engine running for a while. High speed the blower spins longer, low speed a shorter time, when shut off.
So, that's what's probably going on,I just don't know where you would look to fix it. (sorry) Maybe the ignition switch????
Hope this helps. When you turn or spin a d/c motor it will make voltage.
