So yes, it seems to be related to this.
But: we're not exactly using HA. We have a single VM (that is on proxmox1) set up as an HA resource as an experiment.
Everything else is VMs / CTs living on one or the other box using no HA features at all.
I can understand, perhaps, why that single resource might get offlined (but not really, given it was on the node that wasn't shut down), but it's very surprising to me that doing a "shutdown" on proxmox2 nukes every VM without warning, including ones that are just single VMs.
Why does it do that?