Comment 106 for bug 439448

@Chris: I'm sure you're right. My reasoning was the following: this only happens with the indicator applet and no other applet so could it be triggered by something that the indicator applet does that no other applet does? In practice, the indicator applet (or the application notification area for distros that don't have the indicator applet) presents two specific behaviours that differentiate it from other applets:
1. It changes size dynamically.
2. Each element in the notification area has a size that depends on the application that requests it and therefore a display position that depends on a non-trivial set of variables (namely the sizes and positions of all other indicators to its right).

Only one other applet presents behaviour #1, the window list, and none of them (at least in a standard Ubuntu install) present behaviour #2. Therefore, a programming pattern that works well with every applet you have on the desktop may accidentally trigger unexpected behaviour in gnome-panel when used in something significantly more complex like the indicator applet or the notification area.

Now, my experience of programming with gnome-panel (or gtk for that matter) is close to nil so I may be talking complete nonsense. However, being stubborn, I'd like to prove to myself that I'm talking nonsense so I'll see what I can do to investigate my idea and will report here.