jenkins swarm client can setup node description which is reported by Jenkins as unsafe.
This is done with option -description <string> which passes this as node name seen in Jenkins node list.

One example is jenkins-swarm.jar -description "swarm_ip:127.0.0.1" --the : colon char will cause Jenkins to rise error anytime when swarm node configuration is being saved (this leads to no save action). There may be other outcomes with non valid node descriptions.