This is probably related to all components where workspaces are visible. Setting 5 workspaces in config works, and xfce panel shows 5 workspaces when set. However, as soon as I restart xfce (and therefore the panel), I just get 4 (the default?) again - when looking into settings, there are 5 workspaces set. May be just a configuration read problem?
How did you change the number of workspaces? From the settings dialog or from the desktop windowlist menu?
From the settings dialog (xfce-setting-show).
This works fine for me. I have made some changes to the workspaces module, so I hope this may be fix in the next pre-release.
I'm setting this to FIXED now, please reopen when it still happens with RC1.