@BizJetJock
Interesting, I hadn't really considered an engine hanging after the starter disconnects. The starter disconnects once the engine has become self sustaining (40% N2 (ish)on my type). I guess in your example the engine must have gone into a sort of sub-idle condition, from which it wasn't able to accelerate to ground idle, but equally was able to sustain momentum without the starter?
Did it run down once the starter had dissengaged?