In the UI, after selecting two interfaces to create a network bond, app hangs and loads forever

In MAAS UI, after selecting two interfaces to create a network bond, app hangs and loads forever.

I'm using Debian packages version maas/focal,now 1:3.1.0-10901-g.f1f8f1505-0ubuntu1~20.04.1 all [installed]

I'd like to deploy a machine with particular network settings via MAAS. The machine was commissioned successfully. Before deployment, I want to create a network bond from two interfaces.

I was able to do it for two other interfaces successfully. But for the other two, after selecting them and clicking 'Create bond' it hangs. The only difference I can see between the interfaces I managed to bond and the interfaces that I don't seem to be able to bond, is that the interfaces that I cannot bond are disconnected.

Steps to reproduce:
1. Prepare a machine. Make sure it has at least 2 different NICs with at least 2 ports each.

2. Connect network to the two ports of the first NIC. In the other NIC, leave all ports disconnected.

3. Commission the machine.

4. Go to network settings. Try to create a bond out of the two connected interfaces. That should work.

5. Try to create a bond out of the two interfaces that have no cables connected. That shouldn't work. As soon as you click 'Create bond', the app hangs forever. (screenshots attached)