It seems like Bug 4222 may be relevant or related to this, but...

When I have two basically identically configured RHEV clusters, say old-hosts and new-hosts, I altogether lose the ability to select the Network from the dropdown menu in the Network Interface section of the Virtual Machine tab in the New Host page.

This is only the case if both clusters attach to the same network segments (let's say rhevm, vlan1, vlan2, and vmstorage). If I have multiple clusters with non-identical network segment configurations (say one has only rhevm and vlan1, and the other has rhevm and vlan2), things work as expected.

The workaround solutions seem to be (1) use a single cluster, or (2) configure the clusters differently from each other. Neither of these options is entirely ideal.

Also, I do not see a method for selecting the specific cluster to which I would like a host added. Was this option incorporated into the fix for Bug 4222?