There's a missmatch between the .configuration API vendored for the HC controller and the one in those older versions of the CPO controller.
The HO computes the hash including "" for that field. The cpo doesn't see the field at all to compute the mcs hash. That'd cause the missmatch.

Slack thread https://redhat-internal.slack.com/archives/C04EUL1DRHC/p1739540592972569?thread_ts=1739527507.065809&cid=C04EUL1DRHC 

    

    1. Create an HostedCluster with ImageConfig set in an 4.17.15
    2. Check NodePool rollout
    3. Ignition is failing