I was using an earlier 4.12 release candidate and generating an image in my ~/manifests/ocpbugs-2968 directory. Then, wanting to confirm an issue did not happen in a newer 4.12 release candidate (rc6)

4.12.0-rc.6

100%

1. Take an earlier release candidate, make install-config.yaml and agent-config.yaml
2. Save a copy of the manifests and run openshift-install agent create image
2. Without clearing the current working directory, use the copy of the manifests to have again the same install-config and agent-config
3. Rung openshift-install agent create image

[celebdor@toni ocpbugs-2968]$ ./openshift-install agent create image
WARNING Capabilities: %!!(MISSING)s(*types.Capabilities=<nil>) is ignored 
ERROR failed to write asset (Agent Installer ISO) to disk: cannot generate ISO image due to configuration errors 
FATAL failed to fetch Agent Installer ISO: failed to fetch dependency of "Agent Installer ISO": failed to fetch dependency of "Agent Installer Ignition": failed to fetch dependency of "Agent Manifests": failed to generate asset "ClusterImageSet Config": invalid ClusterImageSet configuration: Spec.ReleaseImage: Forbidden: value must be equal to quay.io/openshift-release-dev/ocp-release@sha256:9d35e900821980023f2ba4f76822006c40ebed1532dacfb82bb6e3cffa0a91c2 

[celebdor@toni ocpbugs-2968]$ ./openshift-install agent create image
WARNING Capabilities: %!!(MISSING)s(*types.Capabilities=<nil>) is ignored 
INFO The rendezvous host IP (node0 IP) is 192.168.122.10 
INFO Extracting base ISO from release payload     
INFO Verifying cached file                        
INFO Using cached Base ISO /home/celebdor/.cache/agent/image_cache/coreos-x86_64.iso 
INFO Consuming Install Config from target directory 
INFO Consuming Agent Config from target directory 
[celebdor@toni ocpbugs-2968]${code}
Additional info:
{code:none}
The issue is that the ClusterImageSet asset does not depend on anything, so the previously generated one in .openshift_install_state.json is kept. It points to a different release image and that fails the validation that prevents users from trying to generate an image with a non-matching binary.