LXPanel crashes when an app that has the urgent notification set multiple times is focused then closed, often while xscreensaver is activated.
For example, Thunderbird with the Lightning extension. When a Lightning event notification window pops up, often when xscreensaver is running, the Thunderbird button in the task-manager will blink, indicating urgent notification. When the Lightning event notification is closed, the Thunderbird button will still be blinking, still indicating an urgent notification. Sometimes the button will blink wildly, many times a second if the notification window has refreshed itself multiple times. When the Thunderbird app is focused, then closed, LXPanel will crash with a segfault:
416 Segmentation fault (core dumped) lxpanel