Issue 6.2.1 is no longer an issue
Issue 6.2.1 (Xfce panel window buttons are not refreshed when a window changes viewport) was fixed in xfce4-panel version: 4.14.4, 2 years ago. Ref. migrated bug report: https://gitlab.xfce.org/xfce/xfce4-panel/-/issues/93. I also verified this on my own computer running xfce4-panel 4.18.4, with both compiz version 0.9.14 and compiz-core version 0.8.18.
Any objections to deleting the issue?