1) if you have only one window (say a terminal) on a workspace by itself on the primary and if you move it to the secondary, it tries to delete the workspace below, (which I guess is fine) but it brieflys shows the first workspace briefly before showing some sliding animation.  I did this with 3 worksapces.

2) If you delete the last window on the primary window while having an application in the secondary window, shell will go to overview.  This is a bit tricky, since this is correct behavior but in a multi monitor context it feels a lot more awkward since for instance I might have a mail client that I'm looking at while doing work on the primary window..  since that's the workspace that is fixed, a lot of people will be tempted to put applications like gimp, libreoffice and what due to it being persistent.  I have no idea how to resolve this.  It probably needs to be a bug by itself.

This doesn't seem to be being used any more.