backupRepositories not working when using a customized Solr.xml

So apparently it's a known issue that if you start customizing the solr.xml file for your sorlcloud cluster various customizations provided by the solr-operator no longer work.
One of these is the backupRepositories feature.
Maybe we could be a bit more clear and add that somehow to the status of the statefulset that some features were skipped as we uploaded a custom solr.xml.
It's completely unclear right now what is going on... as the statefulset even has an annotation that it has backupRepositories....
If you try to backup to that repository it reports that the backuprepository does not exist.

Start by reproducing the backupRepositories behavior with a customized solr.xml, then trace how the StatefulSet status and annotations report that configuration. The work is done when skipped operator features are clearly reported and the status no longer suggests that an unavailable backup repository exists.

Written by the indexing model from the issue text.