Comment 19 for bug 1211276

Zane,

The way this is implemented in https://review.openstack.org/#/c/43173/, if the stack is IN_PROGRESS but the engine doesn't respond confirming that it's still alive, we'll fall back on the current single-engine behavior. Here's a table showing exactly what this patch affects:
http://paste.openstack.org/raw/44891/

In the case of "UPDATE during DELETE", a "State invalid for UPDATE" error would be raised.