Created attachment 7384 screenshot Icons with transparency in the notification area (i.e. all of them) are not rendered correctly in panel 4.13.1, when Xfwm4's compositor is disabled. The background is either solid black, or retains elements of images that were previously visible on it. This problem doesn't appear when the compositor is enabled. See attached screenshot
The way the transparency is implemented here (and as far as I understand it) it relies on the compositor here and I don't want to write a lot of fallback code for fake transparency. I would consider this a WONTFIX for now.
I think I misinterpreted this report. It's not a wontfix, but something that broke during the Gtk3 transition. In part due to a bug in Gtk3, in part due to a bug in Xfce. *** This bug has been marked as a duplicate of bug 14577 ***