Description of problem:

Open the OCP Web Console and:

1. Virtualization
2. Catalog
3. Select 8.x
4. Click 'Customize Virtual Machine'
5. Click Review and Create
6. Go to Disks tab
7. Edit rootdisk
8. Change Source to "Use an existing PVC"
9. Select a PVC (does not matter if already bound or not)
10. Click Save

It fails to change with this.

An error occurred
Error "spec.template.spec.volumes[0] must have exactly one source type set" for field "spec.template.spec.volumes[0]".

The workaround is to delete the Disk and create a new one.

Version-Release number of selected component (if applicable):
4.11.20

How reproducible:
Always

Steps to Reproduce:
As above