Since a few weeks, the XFCE panel is automatically set "always on top" and can not be overlapped by moving or resizing windows : it automatically sets a desktop margin on the side it stands. However, the "Margins and Workspaces" plugin in the XFCE configuration window does not reflect this margin : all margins are set to 0. This behavior is probably not what a user might expect : I think the appropriate margin should be set accordingly to the XFCE panel position & margin (I guess it should not be so difficult as the _NET_WM_STRUT_PARTIAL atom contains necessary values).
It's different things, margins are user defined. Struts are defined by the apps and depend on the window being shown at a given time. I disagree with this bug, there is no inconsistency.
Oh, and it's definitely not a "major" bug!
This is probable fixed in the new version(4.4) if not, please reopen this bug...