Thank you for your report! Unfortunately, I’m having some trouble reproducing this problem.
By “move the viewport”, do you mean navigating in the viewport (i.e, pan, zoom, and rotate in the viewport), or docking the viewport panel in a different place?
I’m working at getting you reproduction steps but it’s something obscure. I’ve seen it a couple times now so it’s not a one-off.
This morning I was writing up tutorial for internal use, and Sequoia was behaving flawlessly - darn!