Sometimes when I log in, Xfce (4.10, on Xubuntu-14.04) doesn't look right at all – the colour theme is an odd mixture of the correct settings (Xfce-darkness, in my case) and what's presumably the Xubuntu defaults.
This happens in an estimated 5% of all logins (with no apparent systematic relationship to parameters such as whether networking is available, recent updates, mains vs. battery power etc.). Sometimes the theme suddenly flips to the correct one a few seconds after the programs in the session are loaded, sometimes it doesn't happen at all.
If I log out and in once more, everything is right again.
What could be the reason for this, and how can I force the correct theme to be loaded without switching to another theme and back, or logging out and in again?