Bug Camera viewport broken

I'm using unity 2021.3.11f1 with URP. In the URP sample scene, if I have 2 base cameras, one set to priority 1 the other to 2, with uninitialized background I get the correct output.

If I then set the viewport settings to different values (e.g. one may stay default, the other has a small nudge), the display breaks: higher priority camera no longer displays lower priority camera in it's active viewport.

It's interesting that if the viewports are the same but non default, it still works.

Anyone know a workaround? I have my highest priority camera show the GUI buttons, lower priority cameras show the scenes in different viewports. I can't use overlay feature because GUI buttons don't want to have any post-processing (e.g. bloom), but scene does and overlay doesn't allow me to do that.