When an app is deployed via the deployments/ dir, but fails for some reason, it is marked as failed with a .failed marker and undeployed. When the AS is rebooted, it tries to redeploy the failure. If this deploy also fails, this new deployment isn't undeployed, and a .deployed marker is written to deployments.

This is with the 7.2.0.Final used in Immutant, I've yet to try to build Immutant on top of 8.x.