Sometimes when I login, I see that the applets (notification area, evolution applet, session applet, indicator applet and workrave applet) are jumbled up - they appear in some random order.
Only change I remember doing recently is to delay execution of startup applications as described here
If your panel is jumbled up, you can try reloading the panel by running the following command in a terminal or the Alt+F2 run dialog:
Have you recently change you monitor setup? Whenever I switch between and external monitor and the internal monitor the applets are usually jumbled.
To fix it, right-click on the all the applets and make sure "Lock to Panel" is not selected. Now, right-click on all the applets and click move. Drag you mouse to the place you wish for the applets you want moved, then click.
It is indeed a problem with attaching an external monitor of a different resolution and going between that and the default screen.
I switch monitors frequently and my applets always get jumbled like crazy, whether locked or not, even if I refresh it.
What I finally did was moved everything to Avant Window Manager since it scales with my resolution and doesn't mess up from changing monitors.